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Introduction: Daratumumab (DARA) is a human, CD38-targeting, IgG1κ monoclonal antibody approved as monotherapy in relapsed/refractory multiple myeloma (RRMM) and in combination with standard of care for RRMM and NDMM. The addition of DARA to standard-of-care regimens in phase 3 studies has consistently improved progression-free survival (PFS) and led to deep and durable responses, including higher rates of minimal residual disease (MRD) negativity compared with standard of care. In the primary analysis of the phase 3 MAIA study (median follow-up, 28.0 mo), D-Rd vs Rd significantly improved PFS and MRD-negativity rates in transplant-ineligible NDMM (Facon T, N Engl J Med 2019). With longer follow-up (36.4 mo), D-Rd maintained a PFS benefit and deeper and more durable responses vs Rd alone (Bahlis N, Blood 2019. 134[Suppl 1]:1875). Here, we report updated efficacy and safety findings from MAIA after approximately 4 years of follow-up. Methods: Patients with NDMM ineligible for high-dose chemotherapy and autologous stem cell transplantation due to age ≥65 years or comorbidities were randomly assigned (1:1) to receive Rd ± DARA. Stratification factors included International Staging System stage (ISS [I vs II vs III]), region (North America vs other), and age ( Results: A total of 737 patients were randomized (D-Rd, n = 368; Rd, n = 369). Patient baseline characteristics were well balanced between the two treatment arms. Median (range) age was 73 (45-90) years, with 44% of patients ≥75 years of age. 27%, 43%, and 29% of all patients were ISS stage I, II, and III, respectively. Among 642 patients evaluable for FISH/karyotyping analysis, 86% had standard and 14% had high cytogenetic risk. After a median follow-up of 47.9 months, 176 (48%) and 273 (75%) patients discontinued study treatment in the D-Rd vs Rd groups, respectively, with 85 (23%) and 113 (31%) patients discontinuing treatment due to progressive disease. PFS remained improved for D-Rd vs Rd (median, not reached [NR] vs 34 mo; HR, 0.54; 95% CI, 0.43-0.67; P Grade 3/4 treatment-emergent adverse events (TEAEs; D-Rd/Rd) occurring in ≥10% of patients were neutropenia (53%/37%), pneumonia (18%/11%), anemia (16%/21%), lymphopenia (16%/11%), hypokalemia (12%/10%), leukopenia (11%/6%), and cataract (11%/10%); grade 3/4 infection rates were 40%/29%. The most common serious TEAE was pneumonia (17%/11%). 11% of patients in the D-Rd arm and 22% in the Rd arm discontinued treatment due to an adverse event. The complete updated data set will be presented at the meeting with additional efficacy endpoints, including MRD-negativity rate. Conclusion : After 48 months follow up, the addition of DARA to Rd continues to demonstrate a superior PFS benefit. More patients continued to have deeper and more durable responses with D-Rd vs Rd alone. No new safety concerns were observed with longer follow-up. These results continue to support the use of D-Rd in the first line of treatment for patients with transplant-ineligible NDMM. Disclosures Kumar: Sanofi: Research Funding; Carsgen: Other, Research Funding; Cellectar: Other; Celgene/BMS: Other: Research funding for clinical trials to the institution, Consulting/Advisory Board participation with no personal payments; Genentech/Roche: Other: Research funding for clinical trials to the institution, Consulting/Advisory Board participation with no personal payments; Takeda: Other: Research funding for clinical trials to the institution, Consulting/Advisory Board participation with no personal payments; Janssen Oncology: Other: Research funding for clinical trials to the institution, Consulting/Advisory Board participation with no personal payments; Novartis: Research Funding; Oncopeptides: Consultancy, Other: Independent Review Committee; IRC member; Karyopharm: Consultancy; Merck: Consultancy, Research Funding; Kite Pharma: Consultancy, Research Funding; AbbVie: Other: Research funding for clinical trials to the institution, Consulting/Advisory Board participation with no personal payments; Tenebio: Other, Research Funding; BMS: Consultancy, Research Funding; MedImmune: Research Funding; Genecentrix: Consultancy; Dr. Reddy's Laboratories: Honoraria; Amgen: Consultancy, Other: Research funding for clinical trials to the institution, Consulting/Advisory Board participation with no personal payments, Research Funding; Adaptive Biotechnologies: Consultancy. Facon:Celgene, Janssen, Takeda, Amgen, Roche, Karyopharm, Oncopeptides, BMS, Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Usmani:Abbvie: Consultancy; Janssen: Consultancy, Honoraria, Other: Speaking Fees, Research Funding; Takeda: Consultancy, Honoraria, Other: Speaking Fees, Research Funding; Sanofi: Consultancy, Honoraria, Research Funding; Celgene: Other; GSK: Consultancy, Research Funding; Merck: Consultancy, Research Funding; BMS, Celgene: Consultancy, Honoraria, Other: Speaking Fees, Research Funding; Amgen: Consultancy, Honoraria, Other: Speaking Fees, Research Funding; SkylineDX: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Pharmacyclics: Research Funding; Incyte: Research Funding; Array Biopharma: Research Funding. Plesner:Janssen: Consultancy. Orlowski:Founder of Asylia Therapeutics, Inc., with associated patents and an equity interest, though this technology does not bear on the current submission.: Current equity holder in private company, Patents & Royalties; STATinMED Research: Consultancy; Laboratory research funding from BioTheryX, and clinical research funding from CARsgen Therapeutics, Celgene, Exelixis, Janssen Biotech, Sanofi-Aventis, Takeda Pharmaceuticals North America, Inc.: Research Funding; Amgen, Inc., AstraZeneca, BMS, Celgene, EcoR1 Capital LLC, Forma Therapeutics, Genzyme, GSK Biologicals, Ionis Pharmaceuticals, Inc., Janssen Biotech, Juno Therapeutics, Kite Pharma, Legend Biotech USA, Molecular Partners, Regeneron Pharmaceuticals, Inc.,: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi-Aventis, Servier, Takeda Pharmaceuticals North America, Inc.: Honoraria, Membership on an entity's Board of Directors or advisory committees. Touzeau:Takeda: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Amgen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; GlaxoSmithKline: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Research Funding. Bahlis:BMS/Celgene and Janssen: Consultancy, Honoraria, Other: Travel, Accomodations, Research Funding; Genentech: Consultancy, Honoraria; GSK: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Karyopharm Therapeutics: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria. Goldschmidt:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product:, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Johns Hopkins University: Other: Grants and/or provision of Investigational Medicinal Product; Incyte: Research Funding; University Hospital Heidelberg, Internal Medicine V and National Center for Tumor Diseases (NCT), Heidelberg, Germany: Current Employment; GlaxoSmithKline (GSK): Honoraria; Adaptive Biotechnology: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product, Research Funding; Mundipharma GmbH: Research Funding; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Novartis: Honoraria, Research Funding; Chugai: Honoraria, Other: Grants and/or provision of Investigational Medicinal Product:, Research Funding; Dietmar-Hopp-Foundation: Other: Grants and/or provision of Investigational Medicinal Product:; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product:, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product:, Research Funding; Molecular Partners: Research Funding; Merck Sharp and Dohme (MSD): Research Funding. O'Dwyer:Celgene: Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); BMS: Research Funding; Carrick Therapeutics: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Janssen: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); AbbVie: Consultancy; ONK Therapeutics: Consultancy, Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. Venner:Celgene, Amgen: Research Funding; Janssen, BMS/Celgene, Sanofi, Takeda, Amgen: Honoraria. Weisel:Adaptive: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria; GlaxoSmithKline: Honoraria; Takeda: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria. Hulin:Celgene/Bristol-Myers Squibb, Janssen, GlaxoSmithKline, and Takeda: Honoraria. Karlin:GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, personal fees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, personal fees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, personal fees; Celgene: Other: Personal fees; Sanofi: Honoraria; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support. Preis:Janssen: Other: for factor XI inhibitor. Broyl:Janssen, Celgene, Takeda, Amgen: Honoraria. Hansson:Amgen, Celgene, Takeda, Janssen Cilag: Consultancy. Krevvata:Janssen: Current Employment. Wang:Janssen: Current Employment. Van Rampelbergh:Janssen: Current Employment. Ukropec:Janssen: Current Employment, Current equity holder in publicly-traded company. Uhlar:Janssen: Current Employment, Current equity holder in publicly-traded company. Kobos:Janssen: Current Employment, Current equity holder in publicly-traded company. Perrot:Amgen, BMS/Celgene, Janssen, Sanofi, Takeda: Consultancy, Honoraria, Research Funding.

Introduction The introduction of new treatment regimens has significantly increased the progression free survival (PFS) of newly diagnosed multiple myeloma (MM) patients. However, even with these novel treatments, for some the disease remains refractory, highlighting the need to identify the pathobiology of high-risk MM. In MM patients, high levels of circulating tumor cells (CTCs) is associated with an inferior prognosis independent of high-risk cytogenetics (Chakraborty et al., 2016), suggesting that CTC numbers are a relevant reflection of tumor cell biology. We hypothesized that high levels of CTCs in MM patients are either the result of a transcriptionally distinct tumor clone with enhanced migration capacities, or driven by transcriptional differences present in the bone marrow (BM) tumor cells. To test these hypotheses, we 1) compared MM cells from paired blood and BM samples, and 2) compared BM tumor cells of patients with high and low CTC levels, using single cell RNA-sequencing. Results We isolated plasma cell (PCs) from viably frozen mononuclear cells of paired peripheral blood (PB) and BM aspirates from five newly diagnosed MM patients (0.5%-8% CTCs) to determine the presence of a distinct CTC subclone. We generated single cell transcriptomes from 44,779 CTCs and 35,697 BM PCs. In the total 9 clusters common to BM PCs and CTCs were identified upon single cell data integration, but no cluster specific for either source was detected. Only 25 genes were significantly differential expressed between CTCs and BM PCs. The absence of transcriptional clusters unique to either CTCs or BM PCs, and the transcriptional similarity between these two anatomical sites makes it highly unlikely that CTC levels are driven by the presence of a transcriptionally-primed migratory clone. We next set out to identify possible transcriptional differences in BM PCs from eight patients with high (2-22%) versus thirteen patients with low (0.004%-0.08%) percentages of CTCs. Recurrent high-risk mutations were present in both groups. Single cell transcriptomes were generated from 74,830 BM PCs. Single cell data integration across all patients led to the identification of 8 distinct PC clusters, one of which was characterized by enhanced proliferation as defined by STMN1 and MKI67 transcription. Interestingly, this proliferative cluster was increased in patients with a high percentage of CTCs. Furthermore, cell cycle analyses based on canonical G2M and S phase markers revealed that actively cycling PCs were more frequent in the BM of patients with a high percentage of CTCs (64% versus 30%, p In order to substantiate this, we isolated BM immune cells from the same 21 patients and generated a library of 301,045 single immune cell transcriptomes. This library contained all major immune cell subsets, including CD4 + and CD8 + T cells, NK cells, B cells and monocytes. Comparative analyses of these cell populations in patients with either high or low levels of CTC are ongoing. Conclusion Through single cell transcriptomic analyses, we demonstrate that CTCs and BM PCs are transcriptionally similar. Importantly, we identify increased BM PC proliferation as a significant difference between patients with high and low levels of CTCs, implicating an increased tumor proliferation as one of the potential mechanisms driving CTC levels and MM disease pathobiology. The relation of the BM immune micro-environment to this altered proliferative state is currently under investigation. Disclosures van der Velden: Janssen: Other: Service Level Agreement; BD Biosciences: Other: Service Level Agreement; Navigate: Other: Service Level Agreement; Agilent: Research Funding; EuroFlow: Other: Service Level Agreement, Patents & Royalties: for network, not personally. Sonneveld: SkylineDx: Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Celgene/BMS: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Broyl: Sanofi: Honoraria; Janssen Pharmaceuticals: Honoraria; Celgene: Honoraria; Bristol-Meyer Squibb: Honoraria; Amgen: Honoraria.

Introduction: The 2-part phase 3 CASSIOPEIA study (NCT02541383) investigated the combination of DARA with VTd (D-VTd) in transplant-eligible NDMM pts. D-VTd induction/consolidation (ind/cons) led to increased rates of MRD negativity and prolonged progression-free survival (PFS) compared with VTd (Moreau P, et al. Lancet. 2019;394(10192):29-38). In Part 2, DARA as post-autologous stem cell therapy (ASCT) maintenance significantly improved PFS in pts who received VTd ind/cons. Most common (≥2.5%) grade 3/4 adverse events included pneumonia (DARA: 2.5%; observation [OBS]: 1.4%), lymphopenia (3.6%; 1.8%), and hypertension (3.0%; 1.6%; Moreau P, et al. J Clin Oncol. 2021;39(no. 15_suppl):8004). Here, we present results from a detailed analysis of MRD negativity. Methods: Eligible pts were 18-65 years of age, had NDMM and were ASCT eligible. Pts were randomized 1:1 to 4 (28-day) cycles of pre-ASCT induction and 2 (28-day) cycles of post-ASCT consolidation with D-VTd or VTd (bortezomib, 1.3 mg/m 2 SC on Days 1, 4, 8, 11; thalidomide, 100 mg PO daily; dexamethasone, 20-40 mg IV/PO; ± DARA, 16 mg/kg IV weekly (QW) in Cycles 1-2, Q2W in Cycles 3-6). Pts who completed consolidation and achieved partial response or better were re-randomized 1:1 to maintenance DARA at reduced intensity (DARA, 16 mg/kg Q8W) for a maximum of 2 years, or OBS. Samples were collected for MRD analysis at predefined timepoints from all pts regardless of response to ind/cons and in pts with very good partial response or better during maintenance. The primary MRD assessment methodology was multiparametric flow cytometry during ind/cons and next-generation sequencing during maintenance, each at the 10 -5 threshold. MRD negativity is reported here for pts who achieved complete response or better. Results: 1,085 pts were randomized to ind/cons (D-VTd, n=543 or VTd, n=542) and 886 pts were re-randomized for post-ASCT maintenance (DARA, n=442 or OBS, n=444). The rate of MRD negativity was higher with D-VTd than with VTd following induction (9.2% vs 5.4%; odds ratio [OR], 1.79; P=0.0150) and consolidation (33.7% vs 19.9%; OR, 2.06; P During maintenance, the rate of MRD negativity significantly favored DARA over OBS (58.6% vs 47.1%; OR, 1.80; P=0.0001). In pts who received D-VTd ind/cons, the MRD-negativity rates with DARA and OBS were 64.2% and 57.6% respectively (OR, 1.43; P=0.1037). In contrast, pts who had received VTd ind/cons showed significantly higher MRD-negativity rates during DARA maintenance vs OBS (52.6% vs 35.8%; OR, 2.26; P=0.0002). The rates of sustained MRD negativity in the D-VTd group were not significantly different with DARA vs OBS (1yr sustained: 48.5% vs 41.0%; OR, 1.41; P=0.0885; 2yr sustained: 28.8% vs 21.8%; OR, 1.47; P=0.0789). In the VTd group, the 1-year sustained MRD-negativity rate was significantly higher with DARA vs OBS (35.7% vs 21.4%; OR, 2.22; P=0.0006) but no difference was observed in the 2-year sustained MRD rate (11.3% vs 13.0%; OR, 0.83; P=0.5481). Conclusion: In CASSIOPEIA, the highest and most durable rates of MRD negativity were achieved after D-VTd ind/ASCT/cons and DARA maintenance. Reduced intensity (Q8W) DARA maintenance did not significantly improve MRD negativity compared to OBS in patients treated with D-VTd. In patients treated with VTd, DARA maintenance did improve MRD negativity, but this effect was not long lasting. Longer follow-up is required to assess the potential long-term benefits of sustained MRD negativity for DARA vs OBS after D-VTd. Figure 1 Figure 1. Disclosures Sonneveld: Karyopharm: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; SkylineDx: Honoraria, Research Funding; Celgene/BMS: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Moreau: Amgen: Honoraria; Janssen: Honoraria; Celgene BMS: Honoraria; Sanofi: Honoraria; Abbvie: Honoraria; Oncopeptides: Honoraria. van der Velden: Janssen: Other: Service Level Agreement; BD Biosciences: Other: Service Level Agreement; Navigate: Other: Service Level Agreement; Agilent: Research Funding; EuroFlow: Other: Service Level Agreement, Patents & Royalties: for network, not personally. Hulin: abbvie: Honoraria; Sanofi: Honoraria; Celgene/BMS: Honoraria; Janssen: Honoraria; Takeda: Honoraria. Arnulf: Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celene/BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees. Mohty: Sanofi: Honoraria, Research Funding; Pfizer: Honoraria; Novartis: Honoraria; Takeda: Honoraria; Jazz: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Gilead: Honoraria; Celgene: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria; Astellas: Honoraria; Amgen: Honoraria; Adaptive Biotechnologies: Honoraria. Karlin: Janssen: Honoraria, Other: member of advisory board, travel support; Abbvie: Honoraria; Amgen: Honoraria, Other: travel support and advisory board ; Sanofi: Honoraria; Takeda: Honoraria, Other: member of advisory board; Celgene-BMS: Honoraria, Other: member of advisory board; GSK: Honoraria, Other: member of advisory board; oncopeptide: Honoraria. Macro: Sanofi: Honoraria; GSK: Honoraria; Takeda: Honoraria, Other: Travel accomodation, Research Funding; Janssen: Honoraria, Other: Travel accomodation, Research Funding; Celgen/BMS: Honoraria. Perrot: GSK: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria; Sanofi: Honoraria, Research Funding; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Levin: Roche, Janssen, Abbvie: Other: Travel Expenses, Ad-Board. Delforge: Amgen, Celgene, Janssen, Sanofi: Honoraria, Research Funding. Zweegman: Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Van De Donk: BMS/Celgene: Consultancy, Honoraria; Janssen: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Cellectis: Research Funding; Takeda: Consultancy; Roche: Consultancy; Novartis /bayer/servier: Consultancy. Krevvata: Janssen: Current Employment. Rigat: Janssen: Current Employment, Current equity holder in publicly-traded company. Yang: Janssen: Current Employment. Vanquickelberghe: Janssen: Current Employment. de Boer: Janssen: Current Employment. Kampfenkel: Janssen: Current Employment. Vermeulen: Janssen: Current Employment, Current equity holder in publicly-traded company. Broyl: Celgene: Honoraria; Janssen Pharmaceuticals: Honoraria; Sanofi: Honoraria; Bristol-Meyer Squibb: Honoraria; Amgen: Honoraria. OffLabel Disclosure: The specific regimen combination is not yet approved in the maintenance setting.

Introduction and background Treatment of newly diagnosed Multiple Myeloma (MM) with Bortezomib, Imid and Dexamethasone followed by high-dose therapy and Lenalidomide maintenance has become standard with an estimated progression-free survival (PFS) of 5 years. In the EMN02 collaborative trial VCD induction (Bortezomib, Cyclophosphamide, Dexamethasone) followed by HDM/ASCT or VMP (Bortezomib, Melphalan, Prednisone), followed by VRD consolidation and Lenalidomide maintenance until progression resulted in a median PFS of 57.5 months from start of maintenance at a median follow-up of 73 months (Cavo et al, Lancet Haematol 2020; Sonneveld et al, J Clin Oncol 2021). Patients with progressive disease during Lenalidomide maintenance are defined as double refractory and have limited options for treatment. The present Phase 2 trial was designed to evaluate a salvage treatment of next generation proteasome inhibition and IMId, i.e., Carfilzomib, continuous Pomalidomide and Dexamethasone (KPd) for patients who developed a first progression after treatment in EMN02 The primary endpoint was progression-free survival (PFS). This trial is registered as NTR5349 and EudraCT 2013-003265-34. Methods Patients were eligible if they had PD according to IMWG criteria during treatment in EMN02. Treatment consisted of 8 cycles of KPd, i.e. Carfilzomib (20/36mg/m 2, days 1,2,8,9,15,16) with Pomalidomide (4 mg days 1-21) and Dexamethasone (20mg days 1,2,8,9,15,16). In patients who had not previously received HDM/ASCT, HDM(200 mg/m 2) was administered followed by autologous transplantation with stem cells previously harvested.. Patients who achieved stable disease or better were randomized to receive Pomalidomide 4mg (21/28 days) with or without Dexamethasone 40mg (days 1, 8, 15, 22) in 28 days cycles until progression. Results At the time of the final analysis 112 patients were registered of whom 1 was ineligible. 59% had received prior HDM/ASCT and 41% VMP. Prior best responses in the EMN02 trial were 39% ³CR , 81% ≥VGPR, 96% ≥PR. The median duration of maintenance in EMN02 had been 33 months and median PFS from start of maintenance 59 months. At inclusion adverse risk factors were available in 92/111 patients, ie R-ISS II or III 62%, del17p 14%, t(14;16) 1%, t(4;14) 20%, amp1q 40%. One hundred (90%) of patients had progressed during or within 6 months after discontinuation of Lenalidomide maintenance. 86 (77%) patients completed 8 cycles of KPd, of whom 69(62%) without dose reduction and received continuous Pomalidomide with Dexamethasone (38%) or without (40%). The median time to discontinuation of Pomalidomide w/o Dexamethasone was 17 months (18 vs 15 months, n.s.). In addition, thirty-three of 42 (79%) eligible patients received their first HDM plus ASCT. Time to first response was 2 months. Best response on protocol was 37% ≥CR, 75% ≥VGPR, 92% ≥PR, respectively. At a median follow-up of 40 months (range 9-66 months) median PFS from registration was 26 months. PFS from randomization was 27 months (Pom/Dex) and 18 months (Pom) respectively (HR 0.68, 95%CI 0.41-1.13, p=0.14). 70 (63%) of patients are alive and in follow-up. With Cox regression analysis predefined risk factors including high-risk cytogenetics (HR 1.36, 95%CI 0.80-2.41), prior HDM/ASCT (HR 1.25, 95%CI 0.78-2.01) and duration of prior maintenance >36 months (HR 3.56, 95%CI 1.42-8.96) were not significant. Median overall survival (OS) was 67 months. KPd-emerging grade 3 and 4 adverse events included hematologic (41%), cardiovascular (6%), respiratory (3%), infections (17%) and neuropathy (2%). There were 6 fatal SAEs not related to progression (1 patient cardiovascular). Discussion This Phase 2 trial demonstrates that KPd followed by Pomalidomide until progression is an effective and safe triple drug regimen in second-line for patients who are refractory to Lenalidomide. The benefit is observed across subgroups of risk factors. A 92% overall response and 26 months PFS is clinically relevant in this population and compares favourably to Pom/Vd. Using this regimen HDM/ASCT could be performed in the majority of patients. Acknowledgements This trial was conducted as an investigator sponsored trial by HOVON and the European Myeloma Network EMN and supported by a grant from the Dutch Cancer Foundation and by independent grants and drug supply from Amgen and BMS/Celgene. Disclosures Sonneveld: Karyopharm: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; SkylineDx: Honoraria, Research Funding; Celgene/BMS: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Zweegman: Sanofi: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Cavo: Novartis: Honoraria; Adaptive Biotechnologies: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; GlaxoSmithKline: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Accommodations, Speakers Bureau; Bristol-Myers Squib: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Broyl: Sanofi: Honoraria; Janssen Pharmaceuticals: Honoraria; Celgene: Honoraria; Bristol-Meyer Squibb: Honoraria; Amgen: Honoraria. Corradini: Amgen; Takeda; AbbVie: Consultancy, Honoraria, Other: Travel and accommodations; KiowaKirin; Incyte; Daiichi Sankyo; Janssen; F. Hoffman-La Roche; Kite; Servier: Consultancy; AbbVie, ADC Theraputics, Amgen, Celgene, Daiichi Sankyo, Gilead/Kite, GSK, Incyte, Janssen, KyowaKirin, Nerviano Medical Science, Novartis, Roche, Sanofi, Takeda: Honoraria; AbbVie, ADC Theraputics, Amgen, Celgene, Daiichi Sankyo, Gilead/Kite, GSK, Incyte, Janssen, KyowaKirin, Nerviano Medical Science, Novartis, Roche, Sanofi, Takeda: Consultancy; Novartis; Gilead; Celgene: Consultancy, Other: Travel and accommodations; BMS: Other: Travel and accommodation; Sanofi: Consultancy, Honoraria; Incyte: Consultancy; Novartis, Janssen, Celgene, BMS, Takeda, Gilead/Kite, Amgen, AbbVie: Other: travel and accomodations. Minnema: BMS: Consultancy; Janssen: Consultancy; Cilag: Consultancy; Celgene: Other: Travel expenses; Alnylam: Consultancy; Kite/Gilead: Consultancy. Boccadoro: Janssen and GSK: Membership on an entity's Board of Directors or advisory committees; Sanofi, Celgene, Amgen, Janssen, Novartis, Bristol-Myers Squibb, and AbbVie: Honoraria; Sanofi, Celgene, Amgen, Janssen, Novartis, Bristol-Myers Squibb, and Mundipharma: Research Funding.

Introduction: The introduction of new treatments over the past 2 decades has improved survival outcomes in patients with multiple myeloma (MM), yet MM remains incurable. Despite therapeutic advances, most patients with MM eventually relapse and/or become refractory to treatment, and cycle through standard drug classes of proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), and anti-CD38 monoclonal antibodies (mAbs), becoming triple-class exposed. These triple-class exposed patients represent a population with an urgent unmet clinical need and are a major focus for the development of new therapies. There are currently no prospective data outside of clinical trials on standard-of-care (SOC) in MM patients who progress after these treatment regimens. LocoMMotion (NCT04035226) is the first prospective study to assess the efficacy and safety of real-life SOC treatments in triple-class exposed patients with relapsed/refractory MM (RRMM). Initial analysis at a median follow-up of 3.7 months (range: 0.0-12.7) showed an overall response rate (ORR) of 20.1% (95% CI: 15.0-26.0), with only 5% of patients achieving very good partial response or better. Here, we report updated results from LocoMMotion with a longer median duration of follow-up (7.8 months), along with progression-free survival (PFS) and overall survival (OS) data. Methods: LocoMMotion is a non-interventional study of 246 patients across 10 countries (the US and 9 in Europe) and 75 sites. Patients (aged ≥18 years) with a documented diagnosis of MM were included if they received ≥3 prior lines of therapy or were double-refractory to a PI and IMiD; had measurable disease at screening; received at least a PI, an IMiD, and anti-CD38 mAb with documented progressive disease since their last line of therapy; and had an Eastern Cooperative Oncology Group performance status (ECOG PS) score of 0 or 1. Patient-level data and the most common SOC treatments were collected and analyzed during the study period (August 2019 through October 2020). Real-life SOC treatments were defined as those used in local clinical practice. Responses were assessed per International Myeloma Working Group response criteria. A review committee assessed the ORR (primary objective) of real-life current SOC as well as disease progression for the determination of PFS. Secondary objectives included evaluation of additional efficacy endpoints, including OS, and safety. Results: As of the data cut-off date of March 9, 2021, 246 patients were included with a median follow-up of 7.8 months (range: 0.1-16.9); 23 (9.3%) patients were from the US and 223 (90.7%) were from Europe. Median age was 68 years (range: 41-89), 133 (54.1%) were male, 180 (73.8%) had a baseline ECOG PS score of 1, and median time since initial MM diagnosis was 6.3 years (range: Conclusions: Updated results of this first, prospective study of real-life SOC treatment in triple-class exposed patients with RRMM confirm rapid disease progression after application of salvage therapy and poor outcomes with currently available treatments. New treatment approaches with novel therapies are needed to improve outcomes in this patient population. Disclosures Moreau: Oncopeptides: Honoraria; Amgen: Honoraria; Abbvie: Honoraria; Janssen: Honoraria; Sanofi: Honoraria; Celgene BMS: Honoraria. Weisel: Roche: Honoraria; Oncopeptides: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Consultancy; Novartis: Honoraria; Pfizer: Honoraria. Goldschmidt: Incyte: Research Funding; BMS: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Celgene: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Chugai: Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; GSK: Honoraria; Amgen: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Janssen: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Johns Hopkins University: Other: Grant; Molecular Partners: Research Funding; MSD: Research Funding; Mundipharma: Research Funding; Novartis: Honoraria, Research Funding; Dietmar-Hopp-Foundation: Other: Grant; Sanofi: Consultancy, Honoraria, Other: Grants and/or Provision of Investigational Medicinal Product, Research Funding; Takeda: Consultancy, Research Funding; Adaptive Biotechnology: Consultancy. Delforge: Amgen, Celgene, Janssen, Sanofi: Honoraria, Research Funding. Mohty: Novartis: Honoraria; Astellas: Honoraria; Gilead: Honoraria; Bristol Myers Squibb: Honoraria; Pfizer: Honoraria; Adaptive Biotechnologies: Honoraria; Sanofi: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Takeda: Honoraria; Celgene: Honoraria, Research Funding; Amgen: Honoraria; Janssen: Honoraria, Research Funding. Cavo: Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Accommodations, Speakers Bureau; Adaptive Biotechnologies: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES, Speakers Bureau; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bristol-Myers Squib: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Vij: BMS: Research Funding; Takeda: Honoraria, Research Funding; Sanofi: Honoraria, Research Funding; BMS: Honoraria; GSK: Honoraria; Oncopeptides: Honoraria; Karyopharm: Honoraria; CareDx: Honoraria; Legend: Honoraria; Biegene: Honoraria; Adaptive: Honoraria; Harpoon: Honoraria. Dytfeld: Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen Cilag: Consultancy, Current Employment, Honoraria, Membership on an entity's Board of Directors or advisory committees. Angelucci: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene BSM: Honoraria, Other: DMC; Blue Bird Bio: Honoraria, Membership on an entity's Board of Directors or advisory committees; Menarini-Stemline: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: steering commitee, Speakers Bureau; Vertex Pharmaceuticals: Honoraria, Other: DMC; Crispr therapeutics: Honoraria, Other: DMC; Glaxo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees. Perrot: GSK: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria; Sanofi: Honoraria, Research Funding; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Benjamin: Servier: Honoraria, Research Funding; Allogene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Gileai: Honoraria, Research Funding. Van de Donk: BMS/Celgene: Consultancy, Honoraria; Janssen: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Cellectis: Research Funding; Takeda: Consultancy; Roche: Consultancy; Novartis /bayer/servier: Consultancy. Ocio: MSD: Honoraria; Amgen: Consultancy, Honoraria; Bristol-Myers Squibb/Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy, Honoraria, Speakers Bureau; Sanofi: Consultancy, Honoraria; Karyopharm: Consultancy; Oncopeptides: Consultancy, Honoraria; Pfizer: Consultancy; Secura-Bio: Consultancy. Scheid: Roche: Consultancy; Abbvie: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Gay: Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Honoraria. Rodriguez-Otero: Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Clínica Universidad de Navarra: Current Employment; Celgene-BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kite: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Regeneron: Honoraria. Broyl: Celgene: Honoraria; Janssen Pharmaceuticals: Honoraria; Sanofi: Honoraria; Bristol-Meyer Squibb: Honoraria; Amgen: Honoraria. Potamianou: Janssen: Current Employment, Current holder of stock options in a privately-held company. Sakabedoyan: Janssen: Current Employment. Semerjian: Janssen: Current Employment. Keim: Janssen Research & Development: Current Employment. Strulev: Janssen Pharmaceutica NV: Current Employment. Schecter: Janssen: Current Employment, Current holder of stock options in a privately-held company. Vogel: Janssen Global Services, LLC: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company, Divested equity in a private or publicly-traded company in the past 24 months. Wapenaar: Janssen: Current Employment; Johnson & Johnson: Current holder of individual stocks in a privately-held company. Nesheiwat: Legend Biotech USA: Current Employment. San-Miguel: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, GlaxoSmithKline, Janssen, Karyopharm, Merck Sharpe & Dohme, Novartis, Regeneron, Roche, Sanofi, SecuraBio, and Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees. Sonneveld: SkylineDx: Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Celgene/BMS: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Einsele: Janssen, Celgene/BMS, Amgen, GSK, Sanofi: Consultancy, Honoraria, Research Funding. Mateos: Oncopeptides: Honoraria; GSK: Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bluebird bio: Honoraria; Celgene - Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sea-Gen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Background. Bispecific antibodies that target tumors by engaging innate-like T cell subsets with inherent antitumor activity, such as Vγ9Vδ2-T and type 1 natural killer T (NKT) cells, may combine high therapeutic efficacy with limited off-tumor toxicity. Type 1 NKT cells respond to self and foreign (glyco)lipid antigens presented in the context of the MHC class I like molecule CD1d which is expressed on various malignancies. Vγ9Vδ2-T cells respond to intracellular accumulation of phosphoantigens in cancer cells by sensing conformational alterations in the butyrophilin (BTN) 2A1-3A1 complex. CD1d is expressed by the majority of patients with CLL and MM, while expression in AML is most pronounced on (myelo)monocytic subtypes. Methods. LAVA-051 is a 27kD humanized bispecific single domain antibody (bsVHH) that directly engages CD1d and the Vδ2-TCR chain of Vγ9Vδ2-T cells. The anti-CD1d VHH specifically stabilizes the interaction between CD1d and the type 1 NKT cell TCR and thereby triggers strong activation of type 1 NKT cells (Nature Cancer 2020;1:1054-1065). Vγ9Vδ2-T and type 1 NKT effector cell activation, proliferation, cytokine production and target cell lysis were assessed in in vitro, ex vivo, and in vivo studies. Due to lack of cross reactivity of LAVA-051 with non-human primate (NHP) CD1d and Vγ9Vδ2-T cells, a cross-reactive surrogate bispecific engager was generated to assess tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) parameters. Results. The CD1d-Vδ2 bsVHH LAVA-051 triggers activation of both Vγ9Vδ2-T and type 1 NKT cells (EC 50 4 pM for Vγ9Vδ2-T and 366 pM for type 1 NKT; induction of > 80% degranulation in 4h assays) and mediates potent killing of CD1d expressing tumor cells by engagement of Vγ9Vδ2-T and/or type 1 NKT cells (EC 50 1 pM for Vγ9Vδ2-T and 216 pM for type 1 NKT; > 85% target cell lysis in 16h assays at a low 1:2 E:T ratio). Further, LAVA-051 triggered pro-inflammatory cytokine production, proliferation of Vγ9Vδ2-T and type 1 NKT cells, and exerted substantial antitumor activity against patient AML, CLL and MM cells that express CD1d and improved survival in in vivo T-ALL, AML and MM mouse models. Multiple dose studies in NHP (7 daily doses up to 1 mg/kg iv) showed clear Vγ9Vδ2-T cell engagement and some cytokine release after the first administration, but no clinical, laboratory, or histopathological toxicity. Reflecting the low molecular size of this bispecific engager, PK studies revealed a short plasma half-life which was however compensated for by prolonged (up to 5 days) binding of the engager to peripheral blood Vγ9Vδ2-T cells allowing intermittent dosing. Conclusions. In this study, we demonstrate that the CD1d-Vδ2 bsVHH LAVA-051 triggers activation of both type 1 NKT and Vγ9Vδ2-T cells, which translates directly into antitumor activity. Based on the expression of CD1d in CLL, MM, and AML, the strong preclinical activity of LAVA-051 against CD1d-expresssing tumors, and the favorable tolerability profile of the surrogate engager in NHP, LAVA-051 is currently evaluated in a first-in-human clinical Phase 1/2a study in patients with CD1d-expressing CLL, MM, or AML refractory to prior therapy (NCT04887259). Disclosures Lameris: Lava Therapeutics: Honoraria, Patents & Royalties, Research Funding. Ruben: Lava Therapeutics: Current Employment, Honoraria, Research Funding. Weerdt: LAVA Therapeutics: Research Funding. Roovers: LAVA Therapeutics: Current Employment, Current equity holder in publicly-traded company. van de Donk: Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Cellectis: Research Funding. Broyl: Amgen: Honoraria; Bristol-Meyer Squibb: Honoraria; Celgene: Honoraria; Janssen Pharmaceuticals: Honoraria; Sanofi: Honoraria. Kater: Abbvie: Honoraria, Other: Ad Board, Research Funding; Janssen, AstraZeneca: Other: Ad Board, steering committee, Research Funding; Genmab, LAVA: Other: Ad Board, Steering Committee; BMS, Roche/Genentech: Other: Ad Board, , Research Funding. Riedl: LAVA THerapeutics: Current Employment, Current equity holder in publicly-traded company; Genmab BV: Current equity holder in publicly-traded company. Iglesias: LAVA therapeutics: Current Employment. Winograd: LAVA therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Celgene: Ended employment in the past 24 months; BMS: Current equity holder in publicly-traded company. Adang: LAVA therapeutics: Current Employment, Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees. de Gruijl: LAVA therapeutics: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; DCPrime: Membership on an entity's Board of Directors or advisory committees; Macrophage Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Partner Tx: Membership on an entity's Board of Directors or advisory committees; Idera Pharmaceuticals: Research Funding; ORCA Therapeutics: Patents & Royalties. Parren: Lava Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; Sparring Bioconsult BV: Membership on an entity's Board of Directors or advisory committees; Genmab: Patents & Royalties; Roche: Consultancy. Vliet: Lava Therapeutics: Current Employment, Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Glycostem: Research Funding.

Background: Multiple myeloma (MM) disease progression is influenced by signals from the bone marrow (BM) microenvironment. Recently, we showed that the MM BM is characterized by inflammatory mesenchymal stromal cells (iMSCs) that transcribe MM survival factors and are predicted to recruit proliferating myeloma cells via CCL2-CCR2 interactions (de Jong et al. Nat Immunol. 2021). iMSCs also transcribed high levels of chemokines that can bind to CXCR1 and 2. Myeloid cells are known to express CXCR1/2, and have been implicated in both pro- and anti-tumor responses in various malignancies. Therefore, we hypothesized that iMSCs attract and influence myeloid populations in the MM BM. Results: Using flow cytometry, we verified expression of CXCR1/2 on myeloid cell populations in the BM of 5 newly diagnosed MM (NDMM) patients. CD15 + neutrophils were the most dominant population expressing these receptors, as 22.4% (± 9.8%) of cells expressed CXCR2 alone, and 72.6% (± 8.0%) expressed both CXCR1 and CXCR2. CD14 + monocytes only expressed CXCR2 (86.9% ± 15.8%). Importantly, less than 1% of myeloma cells expressed these receptors (n = 17 NDMM). As these findings suggested neutrophils and monocytes as potential targets of iMSC-mediated chemotaxis, we set out to identify MM-associated alterations in this population by performing single cell RNA sequencing of the full neutrophilic and monocytic lineages (n = 5 NDMM and 2 controls). In line with our flow cytometric data, CXCR1 transcripts were absent in monocytes, while CXCR2 was transcribed by classical monocytes of both myeloma patients and controls. Interestingly, CXCR1 and CXCR2 transcription was increased in mature neutrophils of MM patients compared to controls. Additionally, both mature classical monocytes as well as mature neutrophils of MM patients had an activated transcriptome as defined by increased transcription of C3AR1, SLPI, and IL6R, the plasma cell supportive factor TNFSF13B (encoding BAFF), and the inflammatory cytokines IL1B and IL18. Transcription of IL1B and IL18 can be regulated by pattern-recognition receptors (PRRs) binding damage-associated molecular patterns (DAMPs) resulting from e.g. matrix breakdown. Transcription of PRRs as TLR1, 2 and 4 was increased in mature neutrophils and classical monocytes of MM patients compared to controls. Secretion of IL-1β and IL-18 relies on the cleavage of pro-forms of these cytokines by the inflammasome, a multiprotein complex that is assembled in response to alarmins. Transcription of inflammasome components PYCARD, NLRP3 and CASP1 was increased in mature neutrophils and classical monocytes of patients with MM. Additionally, protein levels of both IL-18 and IL-1β are increased in BM plasma from MM patients, implicating activated neutrophils and monocytes as a potential sources of these cytokines. Conclusion: In MM, mature neutrophils and classical monocytes are activated and might interact with iMSCs via CXCR1 and/or 2. Moreover, these myeloid cells are inflammasome-primed and are likely to be sources of the increased IL-1β levels in the MM BM. Therefore, myeloid cells and iMSCs may form a feed-forward loop in which myeloid cells contribute to a pro-MM environment by maintaining iMSC and by directly providing BAFF to tumor cells. Disclosures Broyl: Celgene/BMS: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Sonneveld: Janssen: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding; SkylineDx: Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Celgene/BMS: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding.

Introduction: Daratumumab (DARA)-based regimens are effective and well tolerated in both newly diagnosed and relapsed/refractory multiple myeloma (RRMM) patients. However, the prognosis for patients who have become refractory to proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs) and DARA is poor. A better understanding of determinants of response and mechanisms of resistance to DARA may lead to new rationally designed treatment strategies. We therefore characterized the effect of DARA on the immune system in MM patients treated with DARA monotherapy in part A of the DARA-ATRA study (ClinicalTrials.gov NCT02751255). Methods: In part A of this prospective multicenter phase 2 trial, 63 DARA-naïve patients were treated with DARA monotherapy (16 mg/kg; approved schedule). Median number of prior lines of treatment was 4 (range 2-11), all patients were previously exposed to lenalidomide and a PI; 89% was refractory to an IMiD, 71% to a PI and 67% to both IMiD and PI. Bone marrow (BM) aspirates obtained at baseline (BL) and at progression (PD; primary refractory, or acquired resistance after prior response) were subjected to deep immune profiling using 28 surface- and intracellular proteins measured by flow cytometry (BL n=51, PD n=47). In a subset of these patients (BL n=39, PD n=33) mass cytometry (CyTOF) was also performed profiling 39 proteins. In addition, peripheral blood (PB) samples obtained at BL (n=44) and PD (n=37) were analyzed using CyTOF. Computational analyses of flow data were performed using UMAP and FlowSOM; CyTOF data were analyzed using SPADE and Freeviz. Statistical analyses included Wilcoxon rank-sum and signed-rank tests, Generalized Linear Mixed Models and ANOVA. Results: A partial response or better was achieved in 41% of patients treated with DARA monotherapy. We compared immune profiles of responding and non-responding (primary-refractory) patients. At BL, the percentages of MM-, T-, B- and NK cells in BM were similar between both groups. However, NK cells of non-responding patients had a lower proportion of CD16 + (P=0.029), and a higher proportion of TIM-3 + (P=0.010) and HLA-DR + (P=0.043) NK cells, suggesting an exhausted phenotype. Non-responders also had a higher proportion of TIM-3 + CD4 + (P=0.022) and TIM-3 + CD8 + T-cells (P=0.004), and a higher proportion of TIM-3 + regulatory T-cells (Tregs) (P=0.042). A higher proportion of TIM-3 + -NK cells, -T-cells, or -Tregs in BM was also associated with poor progression-free and overall survival (PFS; OS). In addition, clinical characteristics associated with poor PFS such as LDH (P=0.016), extramedullary disease (P=0.001) and (R-)ISS stage III (P=0.015) were associated with an increased number of phenotypically exhausted NK- and T-cells. Similar to prior studies, DARA treatment resulted in reduced levels of CD38 on all immune cell subsets and a marked decrease in Tregs, regulatory B cells (Bregs) and NK cells in both BM and PB. Upon acquired resistance, remaining NK cells displayed higher proportions of TIM-3 + (P=0.022), HLA-DR + (P=0.0007) and LAG-3 + (P=0.011), and lower proportions of CD16 + (P=0.002) (Figure 1), compatible with an exhausted phenotype. Furthermore, disease progression was associated with an increase in CD4 + and CD8 + terminally differentiated effector memory T-cells and a decrease in CD4 + and CD8 + central memory T-cells in BM. There was no significant change in the proportion of T-cells expressing immune checkpoint molecules. CyTOF analysis of BM and PB samples confirmed flow cytometric findings. Furthermore, data-driven analysis identified immune profiles specific to progression, including a significant decrease in the fraction of Granzyme B + NK cells, and increase in the fraction of Granzyme B + Bregs at the time of progression. Based on NK cell depletion and -exhaustion observed at PD, we hypothesized that NK cell repletion may restore DARA sensitivity. Indeed, in ex vivo experiments we show that DARA-resistance can be overcome by addition of healthy donor derived NK cells to MM cells obtained from DARA-refractory patients. Conclusion: Here we show that an increased proportion of NK cells with an exhausted phenotype is associated with primary and acquired DARA-resistance, which is in line with the important role of NK cells in DARA-mediated tumor cell elimination ex vivo. Future DARA-based treatment strategies may benefit from reinvigorating NK cells and restoring their cytotoxic capacities. Figure 1 Figure 1. Disclosures Zweegman: Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees. Minnema: Celgene: Other: Travel expenses; Alnylam: Consultancy; Cilag: Consultancy; Janssen: Consultancy; Kite/Gilead: Consultancy; BMS: Consultancy. Broyl: Celgene/BMS: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Levin: Roche, Janssen, Abbvie: Other: Travel Expenses, Ad-Board. Kersten: Kite/Gilead: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria; Roche: Honoraria; Takeda: Consultancy; BMS/Celgene: Consultancy; Miltenyi Biotech: Consultancy. Krevvata: Janssen: Current Employment. Casneuf: Janssen: Current Employment. Abraham: Janssen: Current Employment. Verona: Janssen: Current Employment. Smets: Janssen: Current Employment. Vanhoof: Janssen: Current Employment. Cortes-Selva: Janssen: Current Employment. van Steenbergen: Biolizard working for Janssen: Current Employment. Vieyra: Janssen: Current Employment. Sonneveld: Karyopharm: Consultancy, Honoraria, Research Funding; SkylineDx: Honoraria, Research Funding; Celgene/BMS: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding. Mutis: Janssen: Honoraria; Genmab: Research Funding; Takeda: Research Funding; Novartis: Research Funding; ONK Therapeutics: Research Funding. van de Donk: Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Cellectis: Research Funding; Servier: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Introduction: The multicentre, randomized, open-label, phase 3 EMN02/HO95 study for patients with newly diagnosed multiple myeloma (NDMM) included two randomization stages (1:1) to (R1) intensification therapy with either upfront ASCT or bortezomib-melphalan-prednisone (VMP), and thereafter to (R2) consolidation therapy or no consolidation, followed by lenalidomide maintenance in both arms. Results of the final analysis from R1 (M. Cavo et al. Lancet Haematol. 2020, 7, e456-68) showed that at a median follow-up of 60.5 months progression-free survival (PFS), the primary study endpoint, was significantly improved with ASCT compared with VMP (median, 57 versus 42 months; HR 0.73, 95% CI 0.62-0.85, adjusted p=0.0001). However, no difference between these groups was found in terms of overall survival (OS), a secondary endpoint (HR 0·90, 0·71-1·13, adjusted p=0·35). Methods: We performed an updated analysis of the study with longer-term follow-up. Efficacy endpoints included OS, PFS on next-line therapy (PFS2), and time to next treatment (TTnT). Analyses were restricted to patients randomized to either ASCT (n=702) or VMP (n=495). Clinical outcomes of patients randomized to upfront ASCT or receiving ASCT at the time of progression after primary randomization to VMP (delayed ASCT) were also explored. Results: At an extended median follow-up of 75 months (IQR 67-84), patients randomized to ASCT had a significantly longer OS than those randomized to VMP (Figure). Median OS was not reached in both arms, and the 75-month survival estimate was 69% (95% CI 65-73) in the ASCT group versus 63% (95% CI 59-68) in the VMP group (HR 0.81, 95% CI 0.66-0-98, adjusted p=0.034). Patients who benefited the most from randomization to ASCT were those with unfavourable prognostic characteristics at baseline, including ISS disease stage 2-3 (HR 0.78, 95% CI 0.61-0.99, p=0.047), R-ISS stage 2-3 (HR 0.79, 95% CI 0.62-0.99, p=0.042), and the presence of at least one of the following cytogenetic abnormalities on FISH analysis: t(4;14) and/or t(14;16) in ≥10% CD138-positive plasma cells, and/or del(17p) in ≥20% enriched plasma cells. Overall, the 75-month OS estimate for patients with a high-risk cytogenetic profile was 54% with ASCT versus 39% with VMP (HR 0.61, 95% CI 0.42-0.89, p=0.010). The magnitude of OS benefit with ASCT, as measured by the HR value, was the highest for patients with del(17p) positivity (HR 0.49, 95% CI 0.28-0.86, p=0.013). PFS2 from R1 was significantly longer for patients in the ASCT arm than for those in the VMP arm. The 75-month PFS2 estimate was 57% in the ASCT group and it was 49% in the VMP group (HR 0.76, 95% CI 0.64-0.90, adjusted p=0.002) (Figure). Patients randomized to ASCT had a significantly longer TTnT in comparison with those who were randomly assigned to VMP. Median TTnT values for these groups were 66 versus 47 months, respectively (HR 0.71, 95% CI 0.60-0.82, adjusted p Conclusions: Upfront ASCT significantly prolonged OS, PFS2 and TTnT in comparison with VMP in NDMM patients. Figure Disclosures Cavo: Jannsen, BMS, Celgene, Sanofi, GlaxoSmithKline, Takeda, Amgen, Oncopeptides, AbbVie, Karyopharm, Adaptive: Consultancy, Honoraria. Gay:AbbVie: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees. Beksac:Janssen&janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Speakers Bureau; Takeda: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Deva: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Dimopoulos:Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees. Petrucci:GSK: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees. Zweegman:Amgen: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Membership on an entity's Board of Directors or advisory committees; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Zamagni:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Speakers Bureau; Takeda: Honoraria, Other: Travel, Accommodations, Expenses, Speakers Bureau; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Speakers Bureau; Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Speakers Bureau. Palumbo:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Galli:BMS: Honoraria; Celgene: Honoraria; Janssen: Honoraria; Takeda: Honoraria. Maisnar:Janssen, Takeda, Amgen, BMS/Celgene, The Binding Site: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Hansson:Amgen, Celgene, Takeda, Janssen Cilag: Consultancy. Belotti:Celgene: Membership on an entity's Board of Directors or advisory committees; Jannsen: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Offidani:Janssen: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. Zambello:Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees. Liberati:Verastem: Research Funding; Janssen: Honoraria, Research Funding; Takeda: Research Funding; Morphosys: Research Funding; Novartis: Research Funding; GSK: Research Funding; Incyte: Honoraria; Oncopeptides: Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Honoraria, Research Funding; Onconova: Research Funding; Pfizer: Research Funding; Karyopharm: Research Funding. Broyl:Janssen, Celgene, Takeda, Amgen: Honoraria. Musto:Amgen: Honoraria; Celgene: Honoraria. Ludwig:Seattle Genetics: Other: Advisory Boards; Takeda: Research Funding; Sanofi: Other: Advisory Boards, Speakers Bureau; Bristol Myers: Other: Advisory Boards, Speakers Bureau; Amgen: Other: Advisory Boards, Research Funding, Speakers Bureau; Janssen: Other: Advisory Boards, Speakers Bureau; Celgene: Speakers Bureau. Hajek:Roche: Consultancy, Honoraria, Research Funding; Oncopeptides: Consultancy, Honoraria, Research Funding; Pharma MAR: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Waage:Janssen: Consultancy, Honoraria, Speakers Bureau; Takeda: Consultancy; Shire: Honoraria. Mellqvist:Janssen. Celgene, Amgen: Honoraria. Boccadoro:Novartis: Honoraria, Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Mundipharma: Research Funding; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Research Funding; AbbVie: Honoraria; Bristol-Myers Squibb: Honoraria, Research Funding. Sonneveld:Karyopharm: Consultancy, Honoraria, Research Funding; Skyline Dx: Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy; Amgen: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding.

Introduction: Daratumumab (DARA) has potent single agent activity in relapsed/refractory multiple myeloma (RRMM). The effectivity of DARA is partially dependent on the expression of its target, CD38, on tumor cells. Upregulation of CD38 on MM cells by all-trans retinoic acid (ATRA) improved the ex vivo efficacy of DARA, even in DARA-resistant MM cells. We therefore evaluated the efficacy and safety of DARA combined with ATRA in RRMM patients in the DARA/ATRA study (NCT02751255). Methods: In part A of this prospective, multicenter phase 1/2 trial, DARA was administered according to the approved schedule (16 mg/kg; cycles 1-2: weekly; cycles 3-6: biweekly; cycles ≥7: monthly). In part B, ATRA was given twice daily during 3 days prior to each DARA infusion. DARA dosing was resumed according to the aforementioned schedule. Inclusion criteria were ≥2 prior lines of treatment, WHO performance score 0-2, adequate bone marrow reserve, kidney and hepatic function. Patients were enrolled in part B, after treatment in part A, if they developed disease progression (PD), or if they had insufficient response defined as < minimal response (MR) after cycle 2, or < partial response (PR) after cycle 3, and if they still fulfilled the other inclusion criteria. All patients gave written informed consent. In phase 1 of part B, we determined the maximum tolerated dose (MTD) of ATRA (dose levels: 15, 30 and 45mg/m2) and the recommended dose level (RDL) for phase 2. We here report overall response rate (ORR), progression free survival (PFS(A)), overall survival (OS) and adverse events (AEs) for all patients in part A. For patients treated at the RDL in part B, we report ORR, PFS(A), PFS for part A + B combined (PFS(A+B)) and AEs. Results: Between July 2016 and October 2017, 63 patients were enrolled in part A, baseline characteristics are described in Table 1. At data cut-off (July 1st, 2019), 6 patients were still on treatment in part A. The median duration of follow-up of surviving patients at data cut-off was 26 months (range 18.2 - 39.4 months). The ORR in part A was 41% (22% PR, 14% very good PR [VGPR] and 5% (stringent) complete remission; Figure 1). The median PFS(A) and OS from start of DARA for all enrolled patients were 7.0 months (95% CI 5.3-8.8) and 28.2 months (95% CI 20.4-36.0), respectively. Eight patients did not meet eligibility criteria for part B, and 1 patient refused further treatment in part B. In part B phase 1, 14 patients were treated with ATRA at the 3 dose levels. The MTD was not reached and the RDL for phase 2 was defined as 45mg/m2. At data cut-off, 34 patients were enrolled in part B phase 2, of whom 2 patients were still on treatment. Thirty-two patients stopped treatment due to PD (n=28) or withdrawal of consent (n=4). Next, we focused on all 42 patients who were treated at the RDL in part B (8 patients in phase 1, and 34 patients in phase 2). The ORR in part B was 5% (VGPR n=2). However, 57% achieved MR or stable disease (SD; Figure 1). During part A, median PFS(A) in these patients was 6.7 months (95% CI 2.7-10.6). When stratified by ≥PR vs SD/MR vs PD/not evaluable (NE), median PFS(A) was 9.9 months (95% CI 3.1-16.7) vs 3.2 months (95% CI 2.5-3.9) vs 1.2 months (95% CI 0.8-1.5), respectively. Addition of ATRA and re-intensification of DARA in DARA-refractory patients resulted in a median PFS(A+B) of 7.9 months (95% CI 5.6-10.1 months). When stratified by ≥PR vs SD/MR vs PD/NE in part A, median PFS(A+B) was 17.7 months (95% CI 9.6-25.7) vs 5.4 months (95% CI 3.8-7.0) vs 2.5 months (95% CI 2.1-2.9), respectively. The presence of extramedullary plasmacytomas (P=0.004 and P=0.012) and WHO ≥ 1 (P=0.002 and P=0.005) were associated with lower PFS(A) and PFS(A+B). Importantly, combination of ATRA with DARA did not increase the rate of AEs (Table 2). The incidence of any grade infusion related reactions (IRR) was 34.9%. There were no complications with red blood cell transfusions. Conclusion: Here, we report for the first time on the efficacy of DARA re-intensification, combined with ATRA in DARA-refractory patients. Overall, this approach resulted in a modest prolongation of PFS. Patients with primary DARA-refractory disease did not benefit from the addition of ATRA. However, in patients with ≥PR on DARA monotherapy prior to progression, addition of ATRA and re-intensification of DARA was of marked clinical benefit with an additional 7.8 months of disease control. The combination of DARA and ATRA was well tolerated and safe. Disclosures Minnema: Celgene Corporation: Honoraria, Research Funding; Amgen: Honoraria; Gilead: Honoraria; Servier: Honoraria; Jansen Cilag: Honoraria. Levin:Takeda: Membership on an entity's Board of Directors or advisory committees, Other: Educational grant ; Amgen: Membership on an entity's Board of Directors or advisory committees, Other: Educational grant ; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Educational Grant; Roche: Membership on an entity's Board of Directors or advisory committees, Other: Educational Grant; Abbvie: Membership on an entity's Board of Directors or advisory committees, Other: Educational Grant. Broyl:Celgene, amgen, Janssen,Takeda: Honoraria. Bos:Celgene: Research Funding; Kiadis Pharma: Other: Shareholder (of Cytosen, acquired by Kiadis). Kersten:Miltenyi: Honoraria; Mundipharma: Honoraria, Research Funding; Kite Pharma: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Gilead: Honoraria; Amgen: Honoraria, Research Funding; Takeda Oncology: Research Funding; Celgene: Honoraria, Research Funding; Roche: Honoraria, Research Funding; Novartis: Honoraria. Mutis:Janssen Research and Development: Research Funding; Celgene: Research Funding; Onkimmune: Research Funding; Genmab: Research Funding. Zweegman:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding. Sonneveld:SkylineDx: Research Funding; Takeda: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; BMS: Honoraria; Amgen: Honoraria, Research Funding. Van De Donk:Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Servier: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AMGEN: Membership on an entity's Board of Directors or advisory committees, Research Funding. OffLabel Disclosure: ATRA for treatment of MM

Introduction Peripheral neuropathy (PNP) remains one of the most common adverse events during multiple myeloma (MM) treatment. The immunomodulatory agent thalidomide and proteasome inhibitor bortezomib are particularly prone to induce PNP (Dimopoulos MA et al., Leukemia., 2010). Both agents are part of standard treatment regimens for newly diagnosed transplant-eligible MM patients. PNP varies from mild symptoms to severe disability, depending on timely dose reduction or discontinuation of treatment. Currently, incidence or severity of PNP cannot be predicted. Therefore, it is of utmost importance to monitor incidence of PNP in different treatment combinations, and in order to identify risk factors for developing PNP. Aims To investigate the incidence of PNP in patients treated in the Cassiopeia trial, to evaluate the role of CD38 antibody (daratumumab) treatment in development of PNP, and to identify risk factors for the development of PNP. Methods We retrospectively analysed incidence of PNP grade 2 to 4, scored according to common terminology criteria for adverse events version 4 (CTCAE) in the Cassiopeia study, a phase III trial conducted by IFM/HOVON, investigating the efficacy of adding daratumumab to bortezomib, thalidomide and dexamethasone (VTD). 1074 newly diagnosed MM patients were randomised. Patients received 4 induction cycles and 2 post transplantation consolidation cycles of 28 days each. Cycles included subcutaneous bortezomib (1.3 mg/m2 days 1,4,8,11), oral thalidomide (100 mg daily), dexamethasone (20-40 mg) and daratumumab intravenously (16 mg/kg and weekly during induction cycles 1 and 2 and once every two weeks during induction cycles 3,4 and consolidation). This trial was registered as ClinicalTrials.gov NCT02541383 and was supported by the French IFM and Dutch HOVON groups (Moreau et al., Lancet, 2019). Multivariate analysis was performed including sex, age, arm, body mass index (BMI), cytogenetics, ISS stage, country, diabetes mellitus (DM), creatinine clearance, liver function, ECOG, baseline PNP and disease characteristics. Results Baseline characteristics in dara-VTD and VTD arms were similar. Overall, 380/1074 (35%) patients developed grade ≥2 PNP and 102/1074 (9%) patients developed grade ≥3 PNP. Multivariate analysis indicated that the cumulative incidence of PNP grade ≥2 was significantly lower in the dara-VTD arm (33%) when compared to the VTD arm (38%) (hazard ratio (HR)=0.73, 95% confidence interval (CI) 0.59-0.91, P=0.004). Furthermore, risk factors associated with a higher cumulative incidence of PNP grade ≥2 included older age (HR=1.03; P=0.020), grade 1 PNP at baseline (HR= 2.75; P= 0.002) and higher BMI (HR=1.46, P=0.003 for BMI 25-30 to HR=2.02, P=0.004 for BMI > 35). Progression free survival (PFS) from the end of induction was similar (86% vs 80% at 2 years, HR = 0.74, 95% CI 0.41-1.33, P=0.32) for patients developing grade ≥2 PNP during induction (179 pts, 17%). An unexpected finding was the difference in cumulative incidence between countries participating in this trial: in the Netherlands 68/141 (49%) of patients developed grade ≥2 PNP, while in France this was 280/846 (33%) and in Belgium 31/87 (36%) (p The protocol of the Cassiopeia trial included instructions of discontinuation and dose modification, when PNP grade ≥2 was observed. However, in a subset of patients reaching PNP grade ≥ 2 the (temporary) discontinuation or adjustment of dose as described in the treatment protocol had not been applied (respectively in 148/352 (42%) with PNP ≥ 2 and in 39/97 (40%) with PNP ≥3). Conclusions Despite bortezomib being administered subcutaneously and clear instructions on discontinuation and dose modification, we observed a clinically relevant incidence of grade ≥2 PNP (35%) and grade ≥3 PNP (9%) in patients treated in the Cassiopeia trial. Patients in the dara-VTD arm showed less grade ≥2 PNP, suggesting a possible positive effect of daratumumab. Risk factors for the development of grade ≥2 PNP included older age, PNP at baseline and BMI > 25. Differences in incidence between countries were observed, however no clear explanation was found. Furthermore, standard measures for grading PNP, such as CTCAE criteria, are subject to interpretation bias of both the patient and the treating physician. Continuous screening and correct grading of PNP and strict compliance with guidelines is warranted. Disclosures Moreau: Amgen: Consultancy, Honoraria; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Takeda: Honoraria; Sanofi: Consultancy, Honoraria; Novartis: Honoraria. Vermeulen:Janssen: Current Employment, Current equity holder in publicly-traded company. Broyl:Janssen, Celgene, Takeda, Amgen: Honoraria. Sonneveld:Sanofi: Consultancy; Takeda: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding; Skyline Dx: Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding.

This multicenter phase 2 study of the European Myeloma Network investigated the combination of carfilzomib, thalidomide, and dexamethasone (KTd) as induction/consolidation therapy for transplant-eligible patients with previously untreated multiple myeloma (N = 91). During KTd induction therapy, patients received 4 cycles of carfilzomib 20/27 mg/m(2) (n = 50), 20/36 mg/m(2)(n = 20), 20/45 mg/m(2)(n = 21), or 20/56 mg/m(2)(n = 20) on days 1, 2, 8, 9, 15, and 16 of a 28-day cycle; thalidomide 200 mg on days 1 to 28; and dexamethasone 20 mg on days 1, 2, 8, 9, 15, and 16. After autologous stem cell transplantation, patients proceeded to KTd consolidation therapy, where the target doses of carfilzomib were 27 mg/m(2), 36 mg/m(2), 45 mg/m(2), or 56 mg/m(2), respectively, and thalidomide 50 mg. Common grade 3/4 adverse events included respiratory (15%), gastrointestinal (12%), and skin disorders (10%); polyneuropathy was infrequent (1%). Complete response rates after induction and consolidation treatment were 25% and 63%, respectively; rates of very good partial response or better after induction and consolidation were 68% and 89%, respectively. At a median follow-up of 23 months, the 36-month progression-free survival rate was 72%. The KTd induction and consolidation regimens were active, safe, and well tolerated. This study was registered at http://www.trialregister.n1 as #NTR2422.

Introduction Response to treatment in patients with multiple myeloma (MM) is variable. With increasing possibilities of treatment regimens, predictive factors for response are important. Immune modulating agents (IMiDs) require Cereblon (CRBN) for activity. Therefore, the aim of this study was to identify the genes involved in the CRBN pathway which predict the response to therapy with IMiDs. Methods Paraffin embedded bone marrow (BM) biopsies were used from newly diagnosed patients included in HOVON-87/NMSG-18 trial obtained at inclusion. In this trial, elderly patients with MM were randomized between treatment with Melphalan-Prednisone (MP)-Thalidomide (MPT) followed by thalidomide maintenance versus MP-Lenalidomide (MPR) followed by lenalidomide maintenance (Zweegman et al. Blood 2016;127:1109-1116). BM biopsies were stained with a fully automated dual color, bright-field immunohistochemical assay for CRBN, its neosubstrates Ikaros and Aiolos and the downstream targets IRF4 and c-MYC. CD138 was used to identify MM plasma cells in the BM samples. For CRBN, both nuclear and cytoplasmic staining was evaluated. The distribution and intensity of the immunostaining was assessed using the H-score. The H-scores were calculated using the following formula: [1 × (% cells 1+) + 2 × (% cells 2+) + 3 × (% cells 3+)] and range from 0-300 (0-600 for combined cytoplasmic-nuclear CRBN H-score). For the Cox regression analysis H-scores were corrected by dividing these by a factor 100: hazard rates were considered per 100 points increase of the H-score. Protein levels of the CRBN pathway were compared between patients with complete response (CR) or very good partial response (VGPR) vs partial response (PR) and no change/progressive disease (NC/PD). High-risk cytogenetic aberrations (FISH) were defined as having deletion of 17p, and/or translocation t(4;14) and/or t(14;16). Statistical analysis was done using univariate and multivariate Cox regression analysis for progression free survival (PFS) and overall survival (OS), and the Mann-Whitney test for comparing response groups. Kaplan-Meier survival curves were generated to illustrate survival. Results BM samples obtained at diagnosis from 149 patients were evaluated. Seventy-one patients were treated in the thalidomide arm vs 78 patients in the lenalidomide arm. Median age was 73 years [range 60-90]. Revised ISS stages I/II/III were 12%/80%/8% respectively. At the time of analysis, median follow up of the 45 patients still alive was 83 months [range 23 - 114 months]. Best response on protocol treatment was sCR/CR in 22%, VGPR in 30%, PR in 36% and NC/PD in 12%. Protein expression across the response groups showed higher nuclear CRBN in patients who responded better (sCR/CR/VGPR; median H-score: 178 (49-273)) compared to patients with a worse response (PR/NC/PD; median H-score: 157 (67-251)), albeit not statistically significant (Mann-Whitney p-value=0.06). Higher H-score of nuclear staining of CRBN was associated with a longer PFS and OS, with a hazard ratio (HR) of 0.52 for PFS (95% confidence interval (CI)=0.37-0.86, p In a multivariate analysis (which included study arm (MPT vs MPR), nuclear CRBN, high-risk cytogenetic aberrations and R-ISS), nuclear CRBN remained independently associated with OS as well as R-ISS and study arm. For PFS, only nuclear CRBN remained statistically significant after backward selection. Despite treatment arm being a statistically significant term in the multivariate Cox model for OS, no relation was found for treatment arm and nuclear CRBN, in terms of OS. Conclusions In this study we demonstrate that higher expression of nuclear CRBN in myeloma cells in BM of patients with MM was associated with a superior PFS and OS. Disclosures Couto: Celgene Corporation: Employment, Equity Ownership, Patents & Royalties. Ren:Celgene Corporation: Employment, Equity Ownership. Wang:Celgene Corporation: Employment, Equity Ownership. Thakurta:Celgene: Employment, Equity Ownership. Zweegman:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding. Broyl:Celgene, amgen, Janssen,Takeda: Honoraria. Sonneveld:Amgen: Honoraria, Research Funding; BMS: Honoraria; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; SkylineDx: Research Funding.

Background: Novel agents such as IMIDs and proteasome inhibitors have substantially changed the therapeutic landscape in the first line treatment of multiple myeloma (MM). Better response rates and prolonged progression-free survival have lead to an improvement in overall survival (OS) with median values well beyond 5 years. Therefore to assess whether first line therapy strategies have an impact on the prognosis for patients with MM, long-term results of clinical trials with follow up covering >10 years are necessary. Methods: The HOVON-65/GMMG-HD4 study is a prospective randomized trial testing bortezomib+adriamycin+dexamethasone (PAD) for 3 cycles as induction prior to high-dose chemotherapy (HDT) and autologous stem cell transplantation compared to vincristine+adriamycin+dexamethasone (VAD) in the control arm. After one (HOVON) or two (GMMG) HDT maintenance was given for 2 years consisting of bortezomib every 2 weeks in the PAD arm and thalidomide 50 mg daily in the VAD arm. The study results were initially reported in 2012 (1) and with a median follow up of 91 months in 2018 (2). In this analysis we present OS results after a median follow up of 137 months. All hazard ratios (HR) are given with 95% confidence intervals (CI). Results: Overall survival at 12 years was 32% (CI 27-37%) in the VAD arm versus 36% (CI 31-41%) in the PAD arm without significant difference in the univariate Cox model (HR 0.87, CI 0.73 - 1.03, p=0. 11 or in multivariate Cox model including ISS stage and treatment arm (HR 0.87, CI 0.73 - 1.04, p=0.12; the primary analysis) as specified in the study protocol. When other factors including age, sex, ISS stage, WHO performance status, Immunoglobulin-type, Durie and Salmon-stage, LDH, del 13q, study group and renal impairment (RI, defined as serum creatinine ≥ 2 mg/dl) were added to the Cox model, treatment in the PAD arm was a significant factor for improved OS (HR 0.84, CI 0.7 - 1.0, p=0.048). Of the remaining factors age (HR 1.02, CI 1.01 - 1.03, p=0.002), female sex (HR 0.83, CI 0.69 - 0.99, p=0.044), ISS stage (HR 1.19, CI 1.04 - 1.35, p=0.01), WHO performance status (HR 1.32, CI 1.17 - 1.48, pULN (HR 1.44, CI 1.14 - 1.82, p=0.002), del 13q (HR 1.42, CI 1.17 - 1.73, p Discussion: Long-term results of the HOVON-65/GMMG-HD4 trial show that one third of patients receiving HDT with either thalidomide-based or bortezomib-based maintenance are still alive at 12 years. In contrast to earlier analyses with shorter follow up (1,2) the use of bortezomib in the induction and maintenance treatment provided a significant OS benefit when adjusting for other risk in a multivariate Cox model, although not in the primary analysis. A particular OS benefit was found in patients with RI receiving bortezomib before and after HDT and this could completely abolish the negative prognostic impact of RI. Similarly bortezomib used in combination with tandem-HDT improved OS in patients with del17p so that more than a third of these patients with high-risk MM survived more than 10 years. Our results underline that despite the growing options for treatment at relapse the choice of an optimal first-line therapy is of critical prognostic importance, in particular for patients with high-risk myeloma. References: 1) Sonneveld et al., J Clin Oncol, 2012; 30:2946-2955 2) Goldschmidt et al., Leukemia 2018; 32: 383-390 Figure 1 Disclosures Scheid: Bristol Myers Squibb: Honoraria; Celgene: Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Bertsch:Celgene: Other: travel support; Sanofi: Other: travel support. Zweegman:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding. Weisel:Celgene: Consultancy, Honoraria, Research Funding; Juno: Consultancy; Bristol-Myers Squibb: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria, Research Funding; GSK: Honoraria; Adaptive Biotech: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria. Kersten:Gilead: Honoraria; Kite Pharma: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Novartis: Honoraria; Bristol-Myers Squibb: Honoraria, Research Funding; Mundipharma: Honoraria, Research Funding; Miltenyi: Honoraria; Roche: Honoraria, Research Funding; Takeda Oncology: Research Funding; Celgene: Honoraria, Research Funding. Mai:Mundipharma: Other: travel support; Takeda: Honoraria, Other: travel support, Research Funding; Janssen: Consultancy, Honoraria, Other: travel support; Celgene: Consultancy, Honoraria, Other: travel support. Hillengass:Amgen: Consultancy, Honoraria; Janssen: Honoraria. Stilgenbauer:AbbVie, AstraZeneca, Celgene, Gilead Sciences, Inc., GSK, Hoffmann La-Roche, Janssen, Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau. Broyl:Celgene, amgen, Janssen,Takeda: Honoraria. Bos:Kiadis Pharma: Other: Shareholder (of Cytosen, acquired by Kiadis); Celgene: Research Funding. Dührsen:Amgen: Consultancy, Honoraria, Research Funding; CPT: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Roche: Honoraria, Research Funding; Teva: Honoraria; Novartis: Consultancy, Honoraria; Alexion: Honoraria; Gilead: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Janssen: Honoraria; Celgene: Research Funding. Salwender:Celgene: Honoraria, Other: Travel or accommodations; Sanofi: Honoraria, Other: Travel or accommodations; Takeda: Honoraria, Other: Travel or accommodations; Bristol-Myers Squibb: Honoraria, Other: Travel or accommodations; AbbVie: Honoraria; Amgen: Honoraria, Other: Travel or accommodations; Janssen Cilag: Honoraria, Other: Travel or accommodations. Goldschmidt:Adaptive Biotechnology: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Molecular Partners: Research Funding; Dietmar-Hopp-Stiftung: Research Funding; Mundipharma: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; John-Hopkins University: Research Funding; Amgen: Consultancy, Research Funding; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Chugai: Honoraria, Research Funding; John-Hopkins University: Research Funding; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; MSD: Research Funding; Janssen: Consultancy, Research Funding. Sonneveld:Amgen: Honoraria, Research Funding; BMS: Honoraria; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; SkylineDx: Research Funding. OffLabel Disclosure: bortezomib maintenance thalidomide maintenance

Introduction Primary plasma cell leukemia (pPCL) is a rare and aggressive plasma cell proliferation with a very poor prognosis. The prevalence of poor-risk genetic lesions is higher compared with newly diagnosed multiple myeloma. pPCL requires urgent control of clinical manifestations to prevent early death because of irreversible disease complications. The aim of the EMN12/ HOVON129 study is to improve the outcome of younger and elderly patients with pPCL by incorporating carfilzomib and lenalidomide in induction, consolidation, and maintenance. This trial was registered at www.trialregister.nl as NTR5350. Methods In this ongoing non-randomized, phase 2, multicenter study, patients with previously untreated pPCL receive induction therapy with carfilzomib-lenalidomide-dexamethasone (KRd; 28-day cycles with carfilzomib 20/36 mg/m2 on days 1,2,8,9,15,16; lenalidomide 25 mg days 1-21; dexamethasone 20 mg on days 1,2,8,9,15,16,22,23). In patients ≤65 years, 4 cycles of KRd induction is followed by tandem autologous stem cell transplantation (SCT), KRd consolidation, and then maintenance with carfilzomib (27 mg/m2 on days 1,2,15,16) and lenalidomide (10 mg on days 1-21/28 days) until progression. Patients who are eligible for allogeneic SCT, may also receive autologous-allogeneic tandem transplantation. Patients ≥66 years receive 8 cycles of KRd followed by carfilzomib+lenalidomide maintenance. Supportive care consists of antibacterial-, herpes zoster-, and thrombosis-prophylaxis. Inclusion criteria are newly diagnosed pPCL (>2x109/L circulating monoclonal plasma cells or plasmacytosis >20% of the differential white cell count) and WHO-performance status 0-3. Main exclusion criteria are severe cardiac or pulmonary dysfunction; and creatinine clearance of Here we report the results from the first planned interim analysis for patients aged ≤65 years. The objective of this analysis was to describe overall response rate (ORR) and toxicity of induction therapy for the first 15 registered patients aged ≤65 years. Results From October 2015 till May 2019, we enrolled 33 patients with pPCL, 21 aged ≤65 years and 12 aged ≥66 years. Among the first 15 patients aged ≤65 years, 47% were males; median age was 62 years (range 31-65); 67% had bone disease; and WHO performance status was 2 in 20% and 3 in 27% of patients. Patients had a high tumor burden with a median plasma cell percentage in BM biopsy of 90%. The median peripheral blood plasma cell count was 5.2x109/L (range 2.0-27.4); median platelet count was 121x109/L (range 27-289); and median GFR was 53 ml/min (range 15-81 ml/min). Patients had high-risk disease as evidenced by ISS stage 3 in 67%; elevated LDH in 53%; and high frequency of high-risk genetic lesions (del(17p) in 58%, t(4;14) in 8%, t(14;16) in 8%, del(1p) in 50%, ampl(1q) in 58%). In addition, 20% of patients had extramedullary disease. Among the first 15 registered patients, 14 received the planned 4 cycles of induction treatment, while one patient went off protocol after cycle 3 due to disease progression. After 4 induction cycles, (stringent) CR was achieved by 5 (33%), at least VGPR by 12 (80%), and ≥PR by 14 patients (93%). Table 1 shows adverse events that occurred throughout induction treatment. Adverse events mainly occurred during the first cycle of KRd, and decreased thereafter. Hematological toxicity was limited. One patient experienced a grade 3 infection. Cardiac events occurred in 2 patients: 1 grade 3 myocardial infarction, and 1 grade 2 heart failure. No patients discontinued treatment because of toxicity. Mortality during induction was 0%. In all 21 patients aged ≤65 years, 14 (67%) experienced one or more serious adverse events (SAEs), mainly hospitalizations. The majority of these SAEs occurred during the first KRd cycle (Figure 1). Conclusions KRd induced deep hematologic responses after 4 cycles of therapy (≥VGPR in 80% and ≥CR in 33%) without early death. Toxicity consisted of 20% grade 3 and 27% grade 4 events, occurred mainly during the first cycle of induction, and was manageable with appropriate interventions. In conclusion, KRd provides efficient and rapid disease control, which is essential to prevent early mortality because of irreversible disease complications and to improve survival of patients with this aggressive plasma cell proliferative disorder. Disclosures Van De Donk: Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; AMGEN: Membership on an entity's Board of Directors or advisory committees, Research Funding; Servier: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees. Schjesvold:Novartis: Honoraria; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; SkyliteDX: Honoraria; MSD: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Broyl:Celgene, amgen, Janssen,Takeda: Honoraria. Minnema:Jansen Cilag: Honoraria; Servier: Honoraria; Gilead: Honoraria; Amgen: Honoraria; Celgene Corporation: Honoraria, Research Funding. Offidani:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Caers:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Zweegman:Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Sonneveld:Janssen: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; SkylineDx: Research Funding; BMS: Honoraria; Celgene: Honoraria, Research Funding; Amgen: Honoraria, Research Funding. Hajek:Amgen: Honoraria, Other: Consultant or advisory relationship, Research Funding; Celgene: Honoraria, Other: Consultant or advisory relationship, Research Funding; AbbVie: Other: Consultant or advisory relationship; Bristol-Myers Squibb: Honoraria, Other: Consultant or advisory relationship, Research Funding; Novartis: Other: Consultant or advisory relationship, Research Funding; PharmaMar: Honoraria, Other: Consultant or advisory relationship; Takeda: Honoraria, Other: Consultant or advisory relationship, Research Funding; Janssen: Honoraria, Other: Consultant or advisory relationship, Research Funding. Gay:AbbVie: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees. Vangsted:Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria; Jansen: Honoraria. Musto:Celgene: Honoraria; AMGEN: Honoraria. OffLabel Disclosure: KRd is used for primary plasma cell leukemia

Background: In multiple myeloma, tumor cell survival, disease progression and therapy response are influenced by signals derived from the non-malignant bone marrow niche. This notwithstanding, a detailed in-vivo definition of the cells that define the multiple myeloma niche is lacking. Mesenchymal stromal cells are important niche constituents. Recent progress made with single cell transciptomics suggests that mesenchymal stromal cells are a dynamic population of cells that can exist as several subsets with functionally distinct activation and differentiation profiles. Aim: To identify mesenchymal stromal cell subsets specific for the multiple myeloma bone marrow niche, by comparing stromal cells from myeloma patients to non-cancer controls. Methods: The non-hematopoietic bone marrow niche was isolated from viably frozen bone marrow aspirates from 10 newly diagnosed multiple myeloma patients (6 hyperdiploid, 3 t(11;14) and 1 with deletion of 17p) and 2 non-cancer controls using high speed cell sorting. The purified cells were analyzed by 10X Genomics single cell sequencing directly post-thawing, without prior cell culture. From 10 multiple myeloma patients we generated single cell transcriptomes with an average read-depth of 20,000 reads per cell of in total 12,000 niche cells and from the 2 non-cancer controls a total of 3,500 niche cells. Transcriptomes were pooled and subjected to clustering analyses using the Seurat package for R to identify genetically distinct clusters of niche cells and changes in these clusters associated specifically with multiple myeloma. Results: The bioinformatical analyses generated 10 distinct clusters of niche cells, all of which were present in both non-cancer and multiple myeloma bone marrow. One of these clusters contained CDH5+ endothelial cells while the remaining 9 clusters were subsets of CXCL12+LEPR+ mesenchymal stromal cells. Because samples were taken from the central marrow by aspiration, peripheral endosteal or neuronal lineage cells were not represented in these clusters. Gene Set Enrichment Analysis (GSEA) of the stromal cell clusters from myeloma versus non-cancer controls revealed two significantly altered pathways: TNF signaling via NF-kB and Inflammatory response. Detailed analyses of the individual stromal cell clusters identified two clusters that were responsible for the inflammatory changes identified by GSEA. Both clusters were present in all myeloma patients, constituted on average 20% of total stromal cells and were defined by transcription of the inflammatory chemokines CXCL2, CXCL3 and CXCL8 the cytokine IL6. All these transcripts were absent from the equivalent clusters in control bone marrow. The presence of inflammatory stroma in the multiple myeloma niche indicates either the appearance of a novel stromal cell subset, or activation of pre-existing stromal cells. GSEA analyses suggested inflammatory signaling, and to functionally confirm this, we tested whether activation of stromal cells would induce the inflammatory stromal phenotype. Stimulation of primary human stromal cells in vitro with recombinant TNF was sufficient to induce transcription of CXCL2, CXCL3 and CXCL8, recapitulating the inflammatory transcriptome. Moreover, manual removal of these TNF target genes from the in-silico clustering analyses led to a merging of the inflammatory clusters with non-inflammatory clusters. This indicates that the major distinguishing feature of the myeloma-specific stromal cells are genes induced upon stromal cell activation. Conclusion: Through single cell transcriptomic analyses we have identified the presence of activated inflammatory stromal cells associated with TNF signaling in the multiple myeloma stromal niche. These inflammatory stromal cells are reminiscent of pathogenic cancer-associated fibroblasts found in solid tumors, where these cells create a pro-tumorigenic niche that favors tumor survival and proliferation while simultaneously inhibiting anti-cancer immunity. These findings represent the first description of myeloma-specific stromal cell subsets, and provide novel cellular targets for interventions aimed at disrupting the pro-tumorigenic microenvironment in multiple myeloma. Disclosures Broyl: Celgene, amgen, Janssen,Takeda: Honoraria. Sonneveld:Amgen: Honoraria, Research Funding; BMS: Honoraria; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; SkylineDx: Research Funding; Takeda: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding.

Background: Substantial improvements in both progression free survival (PFS) and overall survival (OS) have been observed in patients with multiple myeloma over recent years. Despite these therapeutic advances, multiple myeloma remains incurable, and most patients eventually progress through standard drug classes of proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), anti-CD38 monoclonal antibodies (mAbs) and others. Understanding the effectiveness of current standards of care in heavily pretreated patients with relapsed and / or refractory multiple myeloma (RRMM) remains an area of unmet need, and there are currently no prospective data reflecting real-world practice in this patient population progressing after PIs, IMiDs and anti-CD38 mAbs. Study design: This prospective multinational efficacy and safety study of real-life current standards of care (real-life SOC) will be conducted in the USA and Europe in approximately 230 adult patients with RRMM who received at least 3 prior lines of therapy or are double refractory to PI & IMiD and have received at least a PI, an IMiD, and CD38 mAbs and with documented progressive disease (PD) since their last line of therapy and have an ECOG score of 0-1. Also, subjects with documented evidence of PD (as above) within the previous 6 months and who are refractory or non-responsive to their most recent line of treatment are eligible. There are no exclusion criteria due to the observational nature of the study. The treatments that these patients receive in real life will be assessed for safety and efficacy over a two-year period. Real-life SOC treatments are defined as the treatment used in local clinical practice by the investigator for adult subjects with RRMM, who meet the eligibility criteria. Subject participation will include a Screening Phase, a Treatment Phase, and a Follow-up Phase up to 24 months from day 1, cycle 1 of the treatment. The Follow-up Phase will continue until study completion, which is defined as 24 months after the last subject receives the first dose of real life SOC treatment. Subjects will be treated until disease progression, unacceptable toxicity, or other reasons. The primary objective of the study is to evaluate the overall response rate (ORR) of real-life SOC treatments in participants with RRMM patients. The secondary and exploratory objectives of the study are the further evaluation of the clinical benefit, patient-reported outcomes (PROs), safety and the potential correlation of rate of minimal residual disease (MRD) negativity with duration of response (DOR), PFS and OS. Methods: Demographic and patient characteristics, clinical response parameters, PRO measures, health care resource utilization, and safety data will be descriptively summarized. Due to the observational nature of the study, there is no direct hypothesis being tested. Therefore, the sample size is based on the clinically acceptable precision of the 95% confidence interval for the primary objective of describing ORR under real-life current SOC treatment. For the primary endpoint exact 95% confidence intervals by the Clopper-Pearson method will be calculated. For therapies available to treat participants with RRMM the reported ORR is 30% or less. When the sample size is 230, using the large sample normal approximation, the width of a two-sided 95% confidence interval for the observed proportion will vary from 0.107 to 0.130 for an expected proportion varying from 0.20 to 0.40. Disclosures Moreau: AbbVie: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. Mateos:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees; EDO: Membership on an entity's Board of Directors or advisory committees; Adaptive: Honoraria; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Weisel:Takeda: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy, Honoraria, Research Funding; GSK: Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Adaptive Biotech: Consultancy, Honoraria; Juno: Consultancy. San-Miguel:Amgen, Bristol-Myers Squibb, Celgene, Janssen, MSD, Novartis, Roche, Sanofi, and Takeda: Consultancy, Honoraria. Facon:Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Boccadoro:Sanofi: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; AbbVie: Honoraria; Mundipharma: Research Funding; Amgen: Honoraria, Research Funding; Janssen: Honoraria, Research Funding. Goldschmidt:ArtTempi: Honoraria; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product, Research Funding; Mundipharma: Research Funding; MSD: Research Funding; Novartis: Honoraria, Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product, Research Funding; Chugai: Honoraria, Other: Grants and/or provision of Investigational Medicinal Product, Research Funding; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product, Research Funding; Molecular Partners: Research Funding; John Hopkins University: Other: Grants and/or provision of Investigational Medicinal Product; Dietmar-Hopp-Foundation: Other: Grants and/or provision of Investigational Medicinal Product; Adaptive Biotechnology: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants and/or provision of Investigational Medicinal Product, Research Funding. Cavo:Janssen, Celgene: Other: Travel Accommodations; Janssen, Celgene, Amgen, Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen, Celgene: Speakers Bureau; Celgene, Janssen, Amgen, BMS, Abbvie, Takeda: Honoraria. Kaiser:Abbvie, Celgene, Takeda, Janssen, Amgen, Abbvie, Karyopharm: Consultancy; Celgene, Janssen: Research Funding; Takeda, Janssen, Celgene, Amgen: Honoraria, Other: Travel Expenses. Gay:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees. Scheid:Janssen: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria; Amgen: Consultancy, Honoraria; Celgene: Honoraria; Takeda: Honoraria, Research Funding. Broyl:Celgene, amgen, Janssen,Takeda: Honoraria. Van De Donk:AMGEN: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees. Potamianou:Janssen-Cilag: Employment. Sakabedoyan:Janssen-Cilag: Employment. Strulev:Jansen Pharmaceutica NV: Employment. Nesheiwat:Legend Biotech: Employment, Equity Ownership. Bergmans:Janssen-Cilag: Employment. Rizvi:Legend Biotech: Employment, Equity Ownership. Pilatowicz:Janssen-Cilag: Employment. Sonneveld:Amgen: Honoraria, Research Funding; BMS: Honoraria; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; SkylineDx: Research Funding.

Introduction and background The treatment of patients with Multiple Myeloma (MM) with relapse or progressive disease after bortezomib, lenalidomide and high-dose therapy represents an important challenge. In the EMN02 collaborative trial newly diagnosed patients with symptomatic MM were randomized to receive VCD induction followed by HDM/ASCT or VMP, followed by a second randomization for VRD consolidation or no consolidation, followed by lenalidomide maintenance until progression (Cavo et al, ASH2017, abstract #397; Sonneveld et al, EHA2018, abstract #108). The present Phase 2 trial was designed for patients with refractory disease or first progression after inclusion in EMN02 in order to evaluate a salvage treatment with next generation proteasome inhibition and IMId, i.e., Carfilzomib, Pomalidomide and Dexamethasone. The primary endpoints were response and progression-free survival (PFS). This trial is registered at www.trialregister.nl as NTR5349 and EudraCT 2013-003265-34. Methods Patients who were included received four 28-days re-induction cycles of KPd, i.e. Carfilzomib (20/36mg/m2, days 1,2,8,9,15,16) with Pomalidomide (4 mg days 1-21) and Dexamethasone (20mg days 1,2,8,9,15,16). In patients who had not previously received HDM/ASCT, HDM(200 mg/m2) was administered followed by autologous stem cell transplantation with stem cells harvested during after induction therapy in the EMN02 trial. Consolidation consisted of 4 additional cycles of KPd, identical to the induction cycles. Patients with stable disease or better received Pomalidomide 4mg w/o Dexamethasone in 28 days cycles until progression. Results At the time of this first planned interim analysis 82 patients were registered and this analysis was performed in the first 60 patients. 48% were randomized prior HDM/ASCT and 42% VMP, and 10% were not randomized. Prior best responses in the EMN02 trial were 35% CR/sCR , 75% ≥VGPR, 97% ≥PR. The median follow-up from inclusion in EMN02 was 43 months (range 21 - 62 months). In 44 patients cytogenetic risk were known, 15 (34%) of them had high-risk FISH (del17p, t(14;16) or t(4;14)). 57 fifty-seven (95%) of patients had progressed during lenalidomide maintenance, 3 patient's data are not yet available. In the present trial 38 (63%) of patients achieved normal completion of treatment according to of the protocol. Twenty patients received their first HDM plus ASCT. Median time on therapy was 14 months. Full dose re-induction treatment according to protocol could be administered in 68% (for Carfilzomib) and 64% (for Pomalidomide) of patients respectively, while for consolidation this was 62% for both Carfilzomib and Best response on protocol was 31% CR/sCR, 65% ≥VGPR, 87% ≥PR, respectively, with no difference according to response on initial treatments. Median time to response (≥PR) was 2 months. At a median follow-up of 16.3 months (range 3 - 32 months) median PFS was 18 months with better outcome in standard risk cytogenetics (HR=0.27 (0.09, 0.83) 95% CIs vs NR) and in patients with prior VMP treatment (HR=0.49 (0.21, 1.16) 95% CIs vs NR). 48 (80%) of patients are alive and in follow-up. KPd-emerging non-hematologic grade 3 and 4 adverse events included cardiovascular (5%), respiratory (5%), infections (20%) and neuropathy (3%). There were 3 fatal SAEs not related to progression (1 patient cardiac failure, 2 patients pneumonia). KPd-emerging hematological toxicity grade 3 and 4 occurred in 30% of patients. Discussion This Phase 2 clinical trial demonstrates that KPd is a feasible, effective and safe triple drug regimen in RRMM patients who have been previously treated and/or are refractory to bortezomib and refractory to lenalidomide. A 87% overall response rate including 31% CR/sCR is clinically relevant in this population. Since median OS has not been reached, longer follow-up is needed. Acknowledgments This trial was conducted as an investigator sponsored trial in EMN and supported by independent grants and drug supply from Amgen and Celgene. Disclosures Sonneveld: BMS: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding. Zweegman:Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene Corp.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Cavo:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Corradini:Roche: Honoraria, Other: Advisory Board & Lecturer; Gilead: Honoraria, Other: Advisory Board & Lecturer; Takeda: Honoraria, Other: Advisory Board & Lecturer; Novartis: Honoraria, Other: Advisory Board & Lecturer; Sandoz: Other: Advisory Board; Amgen: Honoraria, Other: Advisory Board & Lecturer; Abbvie: Honoraria, Other: Advisory Board & Lecturer; Janssen: Honoraria, Other: Lecturer; Sanofi: Honoraria, Other: Advisory Board & Lecturer; Celgene: Honoraria, Other: Advisory Board & Lecturer. Patriarca:Janssen: Other: Advisory role; Celgene: Other: Advisory Role; Travel, accommodations, expenses; Jazz: Other: Travel, accommodations, expenses; MSD Italy: Other: Advisory Role; Medac: Other: Travel, accommodations, expenses. Minnema:Celgene: Consultancy, Research Funding; Janssen: Consultancy; Amgen: Consultancy; Takeda: Consultancy; Servier: Consultancy. Costa:celgene: Employment. Iskander:amgen: Employment. Boccadoro:Mundipharma: Research Funding; Amgen: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; AbbVie: Honoraria; Bristol-Myers Squibb: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Sanofi: Honoraria, Research Funding.

Introduction The introduction of novel drugs has resulted in better outcome in Multiple Myeloma (MM). Disease progression, however, remains a major problem in the majority of patients. Recently, checkpoint inhibitor therapies have been applied, but T cell-mediated control is still poorly understood in MM. Parameters that control local anti-tumour immunity include, among others: presence of immune effector and suppressor cells; immune and metabolic checkpoints; and antigen presentation. These parameters are defined by unique immune markers, and recent technical advances have boosted typing of tumours according to these markers. We set out to evaluate whether overall survival in a large cohort of MM patients is associated with different categories of T cell evasion using transcriptomic analysis. Methods In the current study, we have analyzed gene expression data from 8 large MM trials, with a total number of 1654 patients. The HOVON65/GMMG-HD4, UAMS-TT2, MRC-IX non-intensive, and APEX trials represented a discovery set (1045 patients), whereas the HOVON87/NMSG18, MRC-IX intensive, UAMS-TT3, and UAMS-TT6 trials represented a validation set (609 patients). We defined gene sets for 7 categories of T cell evasion, including: presence of immune suppressor cells, immune checkpoints (and their ligands), metabolic checkpoints, stromal cells and their products, compromised antigen presentation, tumor cell death, and occurrence of oncogenic pathways. Gene expression analysis from pre-treatment bone marrow samples, purified for plasma cells followed 2 stages: first, we obtained ridge regression Cox models for overall survival (OS) for sets of genes that represent T cell evasion in the discovery set which were applied to the validation set; second, we tested each individual gene per gene set versus OS in Cox regression analysis. Bonferroni-Holm multiple testing adjustments were applied. For multivariate analyses age and ISS were included, which were available for all sets, except the TT6 trial. Results Gene models were trained for each gene set in the discovery set. Six models (all except antigen presentation) reached a significant association when applied to the validation set and were used for downstream analyses. The adjusted p values in the multivariate models are: immune checkpoints (and ligands) p= 6.5x10-6, cell death p = 1.9x10-5, oncogenic signaling p = 3.3x10-5, stromal cells and their products p = 3.8x10-5, metabolic checkpoints p = 0. 011, and immune suppressor cells p = 0.020. Analysing individual genes resulted in 34 genes that showed a significant association with OS in the discovery cohort and a remaining 7 genes in the validation cohort. These genes predominantly belonged to the family of immune checkpoint ligands. These genes were VISTA (HR 0.71; CI 0.62-0.82), CD40 (HR 0.75; CI 0.63-0.88), HVEM (HR 0.81; CI 0.71-0.92) and PDL1 (HR 0.78; CI 0.69-0.92). Notably, in a multivariate model, VISTA came out as an independent prognostic marker with a hazard ratio (HR): 0.72 [CI: 0.61-0.83]. Conclusion Immune transcriptomic analysis in a large cohort of patients reveals that OS in MM patients is related to expression of T cell co-signaling ligands, such as VISTA, CD40, HVEM, and PDL1. The expression of the checkpoint molecule VISTA remained independently associated with OS. In addition, another 5 categories of T cell evasion were shown to be significantly related to OS in both a discovery and validation set of patients. Collectively, these results stress the important role of T cell-mediated control of tumor cells in MM patients, and urge for a more detailed analysis in subgroups and individual patients in order to select the most effective (combination) therapies. Disclosures Zweegman: Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene Corp.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding. Gregory:Merck Sharp and Dohme: Research Funding; Amgen: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Honoraria. Sonneveld:Celgene: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; BMS: Honoraria, Research Funding.

Contains fulltext : 88517.pdf (Publisher’s version ) (Closed access) To identify molecularly defined subgroups in multiple myeloma, gene expression profiling was performed on purified CD138(+) plasma cells of 320 newly diagnosed myeloma patients included in the Dutch-Belgian/German HOVON-65/GMMG-HD4 trial. Hierarchical clustering identified 10 subgroups; 6 corresponded to clusters described in the University of Arkansas for Medical Science (UAMS) classification, CD-1 (n = 13, 4.1%), CD-2 (n = 34, 1.6%), MF (n = 32, 1.0%), MS (n = 33, 1.3%), proliferation-associated genes (n = 15, 4.7%), and hyperdiploid (n = 77, 24.1%). Moreover, the UAMS low percentage of bone disease cluster was identified as a subcluster of the MF cluster (n = 15, 4.7%). One subgroup (n = 39, 12.2%) showed a myeloid signature. Three novel subgroups were defined, including a subgroup of 37 patients (11.6%) characterized by high expression of genes involved in the nuclear factor kappa light-chain-enhancer of activated B cells pathway, which include TNFAIP3 and CD40. Another subgroup of 22 patients (6.9%) was characterized by distinct overexpression of cancer testis antigens without overexpression of proliferation genes. The third novel cluster of 9 patients (2.8%) showed up-regulation of protein tyrosine phosphatases PRL-3 and PTPRZ1 as well as SOCS3. To conclude, in addition to 7 clusters described in the UAMS classification, we identified 3 novel subsets of multiple myeloma that may represent unique diagnostic entities.

Recently, cereblon (CRBN) expression was found to be essential for the activity of thalidomide and lenalidomide. In the present study, we investigated whether the clinical efficacy of thalidomide in multiple myeloma is associated with CRBN expression in myeloma cells. Patients with newly diagnosed multiple myeloma were included in the HOVON-65/GMMG-HD4 trial, in which postintensification treatment in 1 arm consisted of daily thalidomide (50 mg) for 2 years. Gene-expression profiling, determined at the start of the trial, was available for 96 patients who started thalidomide maintenance. In this patient set, increase of CRBN gene expression was significantly associated with longerprogression-free survival (P = .005). In contrast, no association between CRBN expression and survival was observed in the arm with bortezomib maintenance. We conclude that CRBN expression may be associated with the clinical efficacy of thalidomide. This trial has been registered at the Nederlands Trial Register (www.trialregister.nl) as NTR213; at the European Union Drug Regulating Authorities Clinical Trials (EudraCT) as 2004-000944-26; and at the International Standard Randomized Controlled Trial Number (ISRCTN) as 64455289.

The aims of this study were to assess the feasibility of prospective pharmacogenomics research in multicenter international clinical trials of bortezomib in multiple myeloma and to develop predictive classifiers of response and survival with bortezomib. Patients with relapsed myeloma enrolled in phase 2 and phase 3 clinical trials of bortezomib and consented to genomic analyses of pretreatment tumor samples. Bone marrow aspirates were subject to a negative-selection procedure to enrich for tumor cells, and these samples were used for gene expression profiling using DNA microarrays. Data quality and correlations with trial outcomes were assessed by multiple groups. Gene expression in this dataset was consistent with data published from a single-center study of newly diagnosed multiple myeloma. Response and survival classifiers were developed and shown to be significantly associated with outcome via testing on independent data. The survival classifier improved on the risk stratification provided by the International Staging System. Predictive models and biologic correlates of response show some specificity for bortezomib rather than dexamethasone. Informative gene expression data and genomic classifiers that predict clinical outcome can be derived from prospective clinical trials of new anticancer agents.

Background We investigated if bortezomib during induction and maintenance improves survival in newly diagnosed Multiple Myeloma (MM). Methods 827 eligible patients with newly diagnosed symptomatic MM were randomized to receive induction therapy with VAD (vincristine, doxorubicin, dexamethasone; n=414) or PAD (bortezomib, doxorubicin, dexamethasone; n=413) followed by high-dose melphalan (HDM) and autologous stem cell transplant (ASCT). Maintenance consisted of daily thalidomide 50 mg (VAD) or 2-weekly bortezomib 1.3 mg/m2 i.v. (PAD) for 2 years. The primary analysis was progression-free survival (PFS) adjusted for ISS stage. We here report long-term results of this trial (P. Sonneveld et al., J Clin Oncol 2012;30:2946-2955). Results The number of eligible patients, patient characteristics and disease characteristics are similar to those reported before. The response rates during protocol treatment have improved slightly since all patients have now completed treatment: CR+nCR 49% vs 35%, VGPR 26% vs 21% and ≥PR 91% vs 83% (PAD vs VAD). After a median follow-up of 67 months, 111 of patients treated with VAD and 131 of patients treated with PAD were progression-free and alive. Progression-free survival (PFS) defined as time from randomization until progression, relapse or death (censored at date of alloSCT, if applicable), was superior with PAD when adjusted for ISS, (HR=0.78, 95% CI [0.66-0.91], P=.002) and in multivariate analysis (HR=0.76 (95% CI [0.64-0.90], P=.001). For the secondary endpoint overall survival (OS) the PAD arm was superior when adjusted for ISS (HR=0.80, 95% CI [0.65-1.00], P=.047) as well as in multivariate analysis (HR=0.78, 95% CI [0.63-0.97], P=.027). Landmark analysis from start of maintenance for PFS did not show a significant difference between Thalidomide and Bortezomib maintenance, however, for OS the PAD arm was superior (P=.035) (HR=0.71, 95% CI [0.52-0.98]). Subgroup analysis performed on patients with renal failure at presentation (serum creatinine ≥2 mg/dL; 45 VAD, 36 PAD) showed that the PAD arm was significantly superior for PFS (HR=0.44, 95% CI [0.26-0.75], P=.003) and OS (HR=0.38, 95% CI [0.21-0.69], P Conclusions Bortezomib during induction and maintenance improves CR and achieves superior PFS and OS. Subgroup analysis after long follow-up confirms the favourable outcome in patients with renal failure. Comparison of study subgroup analysis suggests that bortezomib treatment combined with double intensive treatment may be beneficial for PFS/OS. This trial has been registered as NTR213; EudraCT no. 2004-000944-26; ISRCTN: 64455289. This trial was supported by the Dutch Cancer Foundation, the German Federal Ministry of Education and Research and an unrestricted grant from Janssen-Cilag-Ortho Biotech. The GMMG study group received further grants to support this trial by Novartis, AMGEN, Chugai and Roche. Disclosures: Sonneveld: Janssen-Cilag: Honoraria; Celgene: Honoraria; Onyx: Honoraria; Janssen-Cilag: Research Funding; Millenium: Research Funding; Onyx: Research Funding; Celgene: Research Funding. Salwender:janssen: Honoraria. Weisel:Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria. Schmidt-Wolf:janssen: Research Funding; novartis: Honoraria. van de Velde:Janssen Research & Development: Employment; Johnson & Johnson: Equity Ownership. Lokhorst:Genmab A/S: Consultancy, Research Funding; Celgene: Honoraria; Johnson-Cilag: Honoraria; Mudipharma: Honoraria. Goldschmidt:janssen: Honoraria, Research Funding; amgen: Research Funding; novartis: Honoraria, Research Funding; chigai: Honoraria, Research Funding; roche: Honoraria, Research Funding.

Introduction Multiple Myeloma (MM) is a heterogeneous disease with highly variable survival. Gene expression profiling (GEP) classifiers, such as the EMC-92, can consistently distinguish high risk patients from standard risk patients. Other prognostic factors for MM include the international staging system (ISS) and FISH. Here we present a comparison of prognostic factors and introduce a novel stratification based on EMC-92 and ISS. Methods Scores were calculated for the GEP classifiers EMC-92, UAMS-70, UAMS-17, UAMS-80 and MRC-IX-6 for the following five studies: HOVON-65/GMMG-HD4 (n=328; GSE19784), MRC-IX (n=247; GSE15695), UAMS-TT2 (n=345; GSE2658), UAMS-TT3 (n=238; E-TABM-1138 and GSE2658) and APEX (n=264; GSE9782; for details, see Kuiper R, et al. Leukemia (2012) 26: 2406–2413). FISH data were available for the HOVON-65/GMMG-HD4 trial and the MRC-IX trial. ISS values were available for all datasets except UAMS-TT2. Univariate associations between markers and overall survival (OS) were investigated in a Cox regression analysis, using Bonferroni multiple testing correction. For pair wise analysis of markers, the significance in the increase of partial likelihood was calculated. In order to find the strongest combination (defined as the highest partial likelihood) of GEP-ISS, we compared these pair-wise on the same data. Training sets of classifiers were excluded for those analyses in which that specific classifier was tested. All survival models have been stratified for study. The calculations were done in R using the package survival. Results Prognostic value of FISH, GEP and serum markers was determined in relation to overall survival (Figure 1). GEP classifiers generally performed much better than FISH markers. Of 6 FISH markers with known adverse risk, del(17p), t(4;14), t(14;20) and del(13q) demonstrated a significant association only in one of two data sets with available FISH (HOVON-65/GMMG-HD4). GEP classifiers, on the other hand, are much more robust. Classifiers EMC-92, UAMS-70 and UAMS-80 significantly identify a high-risk population in all evaluated data sets, whereas the UAMS-17 and the MRC-IX-6 classifiers predict high-risk patients in three of four datasets. As expected, ISS staging demonstrated stable and significant hazard ratios in most studies (three out of four). Indeed, when evaluating a merged data set, both ISS and all evaluated GEP classifiers are strong prognostic factors independent of each other. Markers with additive value to each other include all combinations of GEP classifiers as well as the combination of GEP classifiers together with ISS. Tested in independent sets, the EMC-92 classifier combined with ISS is the best combination, as compared to other classifier-ISS combinations tested on the same independent data sets. The strongest risk stratification in 3 groups was achieved by splitting the EMC-92 standard risk patients into low risk, based on ISS stage I, and intermediate risk, based on ISS stage II and III. This stratification retains the original EMC-92 high-risk group, and is robust in all cohorts. The proportions of patients defined as low, intermediate and high risk for this combined EMC-92-ISS classifier are 31% / 47% / 22 % (HOVON-65/GMMG-HD4), 19% / 61% / 20 % (MRC-IX), 46% / 39% / 15 % (UAMS-TT3) and 32% / 55% / 13 % (APEX). Variability in low risk proportion is caused by the variable incidence of ISS stage I. Conclusions We conclude that GEP is the strongest predictor for survival in multiple myeloma and far more robust than FISH. Adding ISS to EMC-92 results in the strongest combination of any of the GEP classifier-ISS combinations. Stratification in low risk, intermediate and high risk may result in improved treatment and ultimately in longer survival of MM patients. This research was supported by the Center for Translational Molecular Medicine (BioCHIP project) Disclosures: van Vliet: Skyline Diagnostics: Employment. Mulligan:Millennium Pharmaceuticals: Employment. Morgan:Celgene: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Millenium: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Merck: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Johnson and Johnson: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees. Goldschmidt:Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Lokhorst:Genmab A/S: Consultancy, Research Funding; Celgene: Honoraria; Johnson-Cilag: Honoraria; Mudipharma: Honoraria. van Beers:Skyline Diagnostics: Employment. Sonneveld:Janssen-Cilag: Honoraria; Celgene: Honoraria; Onyx: Honoraria; Janssen-Cilag: Research Funding; Millenium: Research Funding; Onyx: Research Funding; Celgene: Research Funding.

Abstract 3973 Introduction: Cereblon (CRBN) expression has been described to be essential for the activity of Thalidomide and Lenalidomide. This suggests that presence and possibly increased level of CRBN expression would be associated with better outcome in Thalidomide/Lenalidomide treated patients. The aim of this study was to evaluate CRBN expression in relation to outcome in patients receiving Thalidomide maintenance. Patients and methods: The HOVON-65/GMMG-HD4 trial is a multi-center, phase III trial, comparing Bortezomib in induction and post-intensification vs. conventional chemotherapy and daily Thalidomide 50 mg for 2 years post-intensification in newly diagnosed MM patients. This trial demonstrated that Bortezomib during induction and maintenance improved CR and achieved superior PFS and OS (Sonneveld et al., JCO, July 16, 2012). Gene expression profiling was performed at the start of the trial by Affymetrix U133 Plus 2.0 GeneChip, and was available for 96 patients which started Thalidomide maintenance. CRBN expression levels were based on a combined value of probe sets 218142_s_at and 222533_at. CRBN expression was validated using real-time PCR. All survival analyses were performed in SPSS, with survival time taken from the start of maintenance. Results: In patients receiving Thalidomide maintenance, increased CRBN expression was significantly associated with longer progression free survival (p=0.005, hazard ratio = 0.7) and longer overall survival (p=0.04, hazard ratio= 0.7). Using Kaplan-Meier analysis for visualization and using the median expression to define high and low expression, a significant separation was found for PFS (Log rank p=0.009) but not for OS (Log rank p=0.13). No association was observed between CRBN expression and PFS/OS after Bortezomib maintenance (PFS, p=0.4, hazard ratio=1.1; OS, p=0.7, hazard ratio=1.1). Multivariate Cox regression analysis was performed using the covariates ISS, CRBN and high-risk cytogenetics, defined as having del(17p) and/or 1q gain and/or t(4;14). Higher CRBN levels remained significantly related to longer PFS (hazard ratio 0.7, p=0.03), but not OS (hazard ratio of 0.8, p=0.3). High-risk cytogenetics and ISS were both significant in both PFS and OS multivariate models, with hazard ratios of 2.8 and 3.6, for high-risk cytogenetics and 2.5 and 5.5, for ISS stage 3, respectively (p=0.0004, p=0.003, high-risk cytogenetics and p=0.01 and p=0.005, ISS stage 3, respectively). Conclusion: These data suggest use of CRBN as a biomarker for thalidomide outcome, but further analysis in other Thalidomide trials is required to validate this finding. Disclosures: Lokhorst: Genmab: Consultancy. Sonneveld:Onyx: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; celgene: Honoraria, Research Funding.

Abstract 332 PURPOSE : In Multiple Myeloma (MM), the combination of serum beta-2-microglobulin level with serum albumin concentration has been proposed as an outcome predictor in the International Staging System (ISS). More recently, subgroups of MM defined by genetic and cytogenetic abnormalities have been associated with unique biologic, clinical, and prognostic features. PATIENTS AND METHODS: We analyzed the prognostic value of 12 chromosomal abnormalities by fluorescent in situ hybridization (FISH) in a series of 354 MM patients treated within the HOVON-65/GMMG-HD4 trial. Patients with newly diagnosed MM were randomized to receive either three cycles of VAD (arm A; vincristine, adriamycin, dexamethasone) or PAD (arm B; bortezomib, adriamycin, dexamethasone). All patients underwent autologous stem cell transplantation (ASCT) followed by maintenance therapy with thalidomide 50 mg daily (arm A) or bortezomib 1.3 mg/m2 once every 2 weeks (arm B), respectively. In addition, a second cohort of patients was analyzed as a control group (n=462), undergoing ASCT at the University of Heidelberg between September 1994 and December 2010. RESULTS: For the entire group of patients treated within the HOVON-65/GMMG-HD4 trial, we identified 233 patients with 2 copies (67.7%), 95 patients with 3 copies (27.6%) and 16 patients (4.7%) with more than three copies of the chromosomal region 1q21. In addition to del(17p13) and t(4;14), we added +1q21 (>3 copies) to the group of high-risk aberrations, since the outcome of these patients was almost as poor as it was observed for patients with del(17p13). Subsequently, we analyzed whether combining the ISS score with information on the presence of high-risk aberrations could improve the prognostic value with regard to patients' outcome. A combination of the presence or absence of del(17p13), t(4;14), or +1q21 (>3 copies) with the ISS score allowed patients to be stratified into three distinct groups: low-risk [absence of del(17p13)/t(4;14)/+1q21 (>3 copies) and ISS I], high-risk [presence of del(17p13)/t(4;14)/+1q21 (>3 copies) and ISS II/III], and intermediate-risk (all remaining patients). Most of the patients belonged to the low- (33%) and intermediate-risk (49%) groups, whereas 18% were allocated to the high-risk group. The median PFS times for the low-, intermediate-, and high-risk groups were 41.9 months, 31.1 months (HR=1.7; p=0.0018) and 18.7 months (HR=3.6; p These results were confirmed in the independent cohort of patients: From date of first ASCT, the median PFS times for the low-, intermediate-, and high-risk groups were 43.3 months, 23.0 months (HR=1.5; p=0.015) and 13.8 months (HR=2.4; p=0.0003), respectively. The 4yr-OS decreased from 84% in the low-risk group to 71% (HR=2.1; p=0.0043) and 49% (HR=3.84; p CONCLUSION: In our series, the ISS/FISH-based score/algorithm predicted PFS and OS much better than the ISS alone. Our results with molecular cytogenetic techniques may already have implications for the risk-adapted clinical management of patients with MM particularly in younger patients. Disclosures: van de Velde: Ortho Biotech Oncology Research & Development: Employment. Sonneveld:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen-Cilag: Membership on an entity's Board of Directors or advisory committees, Research Funding; Onyx: Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium: Membership on an entity's Board of Directors or advisory committees.

Abstract 1800 Introduction: Survival of patients with newly diagnosed multiple myeloma (MM) is highly variable and currently used clinical prognostic markers such as the international staging system (ISS) and cytogenetic markers are insufficiently adequate for defining individual patient prognosis. We established a prognostic signature based on gene expression profiling. Methods: The signature was generated using a training set of 290 newly diagnosed MM patients included in the multicenter, prospective open-label randomized phase 3 HOVON65/GMMG-HD4 trial. Gene expression profiles, obtained from purified plasma cells, were generated using the Affymetrix GeneChip® Human Genome U133 Plus 2.0 platform (GSE19784; Broyl et al.,Blood 2010; 14:2543–2553). The model predictive for survival was built by supervised principal component analysis (Bair et al., J. Amer. Statistical Assoc. 2006;101:119–37) and further optimized by simulated annealing. The generated survival signature was compared to six previously reported MM gene expression signatures (i.e. UAMS-70, UAMS-17 (Shaughnessy et al., Blood. 2007;109:2276–84), gene expression-based proliferation index (GPI, Hose et al., Haematol. 2010; 96: 87–95), MRC-IX-6 gene (Dickens et al., Clin. Cancer Res. 2010;16:1856–1864), Millennium (Mulligan et al., Blood 2007; 109:3177–3188) and IFM (Decaux et al., J. Clin. Oncol. 2008; 26:4798–4805). Results: A signature of 92 probe sets (EMC-92-gene signature) was highly discriminative for high-risk MM patients, defined as overall survival (OS) < 2 yr (21.7%) vs. standard-risk MM. This performance was confirmed in independent validation datasets of newly diagnosed MM patients (UAMS-TT2, n=351, GSE2658; MRC-IX, n=247, GSE15695) and relapse MM patients (APEX, n=264, GSE9782). In the UAMS-TT2 dataset, a high-risk population of 19.1% was identified which had a hazard-ratio of 3.52 (P = 2.5 × 10−8). In the MRC-IX study, 20.2% of patients were identified as high risk with a hazard-ratio of 2·38 (P = 3·6 × 10−6; Figure 1a) The high-risk signature was able to identify patients with significantly shorter survival in both the transplant-eligible and non-transplant-eligible patients included in the MRC-IX study. In non-transplant-eligible patients, 23.8% high risk patients were identified with a hazard-ratio of 2.38 (P = 4.3 × 10−4), whereas 17.5% of transplant-eligible patients were high-risk with a hazard-ratio of 2.54 (P = 1.5 × 10−3). The difference between survival in high-risk and standard risk was not restricted to newly diagnosed patients, as 15.9% of patients included in the APEX relapse study were designated high-risk with a hazard-ratio of 3·14 (P = 5·3 × 10−9; Figure 1b). In all sets the signature gave consistent and significant results and had good performance in comparison to other published high-risk gene signatures (Figure 2). In a pair-wise comparison to other high-risk gene signatures the EMC-92-gene showed to be among the top performing signatures and independent of all other signatures. In multivariate analyses, the EMC-92-gene signature proved an independent and superior predictor against clinical and cytogenetic variables such as the ISS and unfavourable cytogenetic aberrations including del(17p). Using the independent MRC-IX set, poor prognostic cytogenetic aberrations 1q gain, del(17p), t(4;14), t(14;16), t(14;20) and del(13q), were enriched in high-risk patients, whereas the frequency of standard risk cytogenetic aberrations such as t(11;14) was lower in the high-risk populations. Although enriched in the high-risk population, still more than half of patients in the standard risk group showed one or more poor prognostic cytogenetic markers Conclusions: We developed a high-risk signature highly discriminative for patients with high-risk versus standard-risk MM, irrespective of treatment regime, age and relapse setting. Use of this signature in the clinical setting may lead to a more informed treatment choice and potentially better outcome for the patient. Disclosures: van Vliet: Skyline Diagnostics: Employment. van Beers:Skyline Diagnostics: Employment, Patents & Royalties. Mulligan:Millennium Pharmaceuticals, Inc.: Employment. Morgan:Millennium Pharmaceuticals, Inc: Honoraria. Gregory:Celgene: Honoraria. Goldschmidt:Johnson& Johnson: Membership on an entity's Board of Directors or advisory committees. Lokhorst:Genmab: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Sonneveld:Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Skyline Diagnostics: Membership on an entity's Board of Directors or advisory committees.

Abstract 302 Background: Multiple Myeloma (MM) is a plasma cell malignancy, characterized by the accumulation of malignant plasma cells in the bone marrow (BM). Prognostic factors in MM include translocations and ISS stage; still, the clinical course is difficult to predict. MicroRNAs (miRNAs) are a class of small non-coding single stranded RNAs involved in posttranscriptional gene regulation, which may be of use in defining MM prognosis and outcome. MiRNAs regulate protein levels by binding to either partially or complete complementary sites in messenger RNAs (mRNAs), leading to translational repression or transcript degradation respectively. In this manner, miRNAs play a role in critical biological processes including cellular growth and differentiation. Specific disease related miRNAs in both acute myeloid leukemia and chronic lymphocytic leukemia have been found with specific miRNA signatures associated with different cytogenetic subtypes. Until now, information available for miRNA expression in MM is limited. Methods: MiRNA expression profiling was performed in 45 newly diagnosed MM patients enrolled in the HOVON-65/GMMG-HD4 trial; a randomized, phase III trial performed to evaluate the efficacy of bortezomib prior to high-dose melphalan (HDM) for response, progression free survival (PFS) and overall survival (OS) in patients with newly diagnosed MM. As controls, four healthy BM samples were obtained from subjects undergoing BM harvest for allogeneic transplantation donorship. For all samples, BM derived CD138 selected plasma cells (PCs) with a minimum purity of > 80% were obtained. RNA was isolated using the miRVANA kit, with subsequent miRNA profiling by TaqMan Human MicroRNA Array v1.0. Unsupervised hierarchical clustering with the centered correlation metric with average linkage was performed using BRB-array tools 3.6.0. For survival analysis, miRNA expression was divided in quartiles: the top quartile vs the rest to identify cases with high expression and the bottom quartile vs the rest for cases with low expression. Log-rank tests for univariate association with PFS and OS were performed for each of the 365 miRNAs using the false discovery rate to correct for multiple testing. Chromosomal abnormalities t(4;14), t(11;14), t(14;16) and deletion 13q14 were determined by FISH analysis. MiRNA expression was compared to mRNA expression, available for 39 out of 45 MM patients, using a Spearman's rank correlation test. mRNA expression was determined by Affymetrix U133 Plus 2.0 arrays (Broyl et al., Blood 2010). Results: Clustering resulted in a dendrogram with 5 clear branches, consisting of 4 MM clusters and 1 normal BM cluster. The MM clusters are characterized by up- and downregulation of distinctive miRNAs: cluster A: upregulation of miRNA clusters miRNA-17∼92 and miRNA-106∼25 (n=23); cluster B: upregulation of miRNA-130a and miRNA-424 (n=8); cluster C: upregulation of miRNA-576 and miRNA-106b (n=9) and cluster D: upregulation of miRNA-372 and miRNA-200a (n=4). An additional cluster of one sample was not defined. MiRNAs predominantly expressed in normal BM were miRNA-28 and miRNA-30c. None of the miRNA clusters correlated with cytogenetic subgroups, i.e. deletion 13q14, t(4;14), t(11;14), and t(14;16) Still, a supervised approach showed significantly higher expression of miRNA-122a, miRNA-33, miRNA-489, miRNA-519e, and miRNA-555 in patients with t(11;14). Upregulation of let-7f, miRNA-194 and miRNA-296 expression were found to be associated with better OS with borderline significance (P = .06). Finally, a significant inverse correlation between miRNA-21 expression and gene expression of two of its validated targets, PDCD4 (P = 2× 10−4) and RECK (P = 8×10−4) was found. PDCD4 is a novel tumor suppressor, whose functions include inhibition of translation through eIF4A/eIF4G. RECK has been shown to be involved in angiogenesis, through inhibition of MMP2 and MMP9. Conclusion: miRNA expression in MM is deregulated compared to normal PCs and MM patients can be classified according to their miRNA expression pattern in four clusters. Furthermore, a trend was found for high expression of miRNAs let-7f, miRNA-194 and miRNA-296 with increased OS. Integration of miRNA and mRNA data shows the putative interaction between miRNA-21 and two of its validated targets; tumor suppressor gene PDCD4 and RECK, suggesting a functional relationship between miRNA expression and development of MM. Disclosures: Sonneveld: Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees; Millennium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees.

Abstract 445 Background. In newly diagnosed myeloma patients, bortezomib treatment induces high rates of complete response (CR) and very good partial response (VGPR). Recently, we published the clustering of gene expression profiles in 320 MM patients, who were included in a large prospective, randomized, phase III transplantation trial with bortezomib (PAD) versus conventional vincristine (VAD) based induction treatment (HOVON65/GMMG-HD4). We identified 12 distinct subgroups CD-1, CD-2, MF, MS, PR, HY, LB, Myeloid, including three novel defined subgroups NFκB, CTA, and PRL3 and a subgroup with no clear gene expression profile (NP). Aim. To look at the prognostic impact of these 12 clusters in the trial and group clusters together into a high risk (HR) and low risk (LR) group in the different treatment arms. Furthermore, to define a high risk signature to identify the patients at increased risk of disease progression. Methods. Gene expression profiles of myeloma cells obtained at diagnosis of 320 HOVON65/GMMG-HD4 patients were available. Response, progression free survival (PFS) and overall survival (OS) data were available for the first 628 patients, resulting in analysis of gene expression in relation to prognosis in 229 patients. The prognostic impact of the genetic subgroups separately and grouped into high and low risk were evaluated using Kaplan Meier and Cox regression analysis using exhaustive search (R). For the high risk gene signature the HOVON65 gene expression data was used as training set with PFS as outcome measure. Two independent myeloma datasets with survival data were used as an external validation, UAMS (GSE2658) and APEX (GSE9782)). The signature was generated by a Cox proportional hazard model in combination with LASSO (Least Absolute Shrinkages and Selection Operator) for simultaneous parameter estimation and variable selection using the R package glmnet. ISS stage was implemented by adjusting the individual covariant penalization factors of the LASSO. Results. The highest CR+nCR rates were found in the PRL3 and NP clusters, i.e. 78% and 86%, respectively (VAD), and 100% (PAD). The lowest CR+nCR rate was 17% in the CD1 cluster (PAD) and 0% in the CD2, MF and PR clusters (VAD). Based on the impact of clusters on PFS and OS in the VAD arm, the MS, MF, PR and CTA clusters were included into a High Risk (HR) group. This HR group showed a median PFS of 13 months and OS of 21 months vs. the Low Risk (LR) group consisting of the remainder of clusters with a median PFS of 31 months and a median OS not reached (P Conclusion. Distinctive gene expression clusters affect prognosis, which differ depending on treatment. In the conventional treatment arm (VAD), MS, MF, PR and CTA clusters confer a worse prognosis while with bortezomib based treatment, only the PR cluster affects prognosis negatively. These HR groups remain independent poor prognostic indicators. Based on the HOVON65/GMMG-HD4 study population, a high-risk signature was generated with strong and highly significant predicting ability in two independent data sets. Disclosures: Mulligan: Millenium: Employment. Goldschmidt:Celgene: Membership on an entity's Board of Directors or advisory committees; Ortho Biotech: Membership on entity's Board of Directors or advisory committees; Ortho Biotech: Research Funding; Celgene: Research Funding; Chugai Pharma: Research Funding; Amgen: Research Funding. Sonneveld:Ortho Biotech: Research Funding; International Myeloma Foundation: Research Funding; Ortho Biotech: Consultancy.

Abstract 304 Background: Bortezomib, a proteasome inhibitor with activity in multiple myeloma (MM) achieves high response rates in newly diagnosed patients. Bortezomib induced peripheral neuropathy (BiPN) affects 15% (grade 3–4) to 40% (grade 1–4) of patients. BiPN frequently is the dose-limiting toxicity which requires dosing adjustments, and significantly influences the quality of life. The pathogenesis of BIPN and the background for the individual differences of susceptibility are largely unknown. Aim: This project was designed to obtain insight in the molecular characteristics underlying BiPN in MM patients. Methods: We investigated the susceptibility to BiPN in 369 patients who were included in a large prospective, randomized, phase III trial (HOVON65/GMMG-HD4) of bortezomib (PAD) versus conventional vincristine (VAD) based induction treatment. The study integrated inherited genetic background as well as the gene expression profile of the myeloma in patients who were closely monitored for BiPN. Genetic variation associated with BiPN was analyzed using a custom-built molecular inversion probe (MIP) based single nucleotide polymorphism (SNP) chip, designed by “Bank on a Cure” (BOAC), containing 3404 SNPs selected in “functional regions” within 983 genes that represent cellular functions and pathways. Gene expression profiles were analyzed in purified myeloma plasma cells (PCs) using Affymetrix 133 Plus 2.0 array and integrated with SNP profiles for an association analysis with BiPN. We used vincristine induced peripheral neuropathy (ViPN) in VAD-treated patients as a reference. Pathway analysis was performed using significant genes (FDR Results: Analysis of myeloma gene expression profiles and SNP data of patients with early onset BiPN (within one treatment cycle) showed an association of genes involved in apoptosis, in nervous system development and in response to oxidative stress. Among the top upregulated genes in myeloma PCs were two enzyme coding genes, RHOBTB2, involved in drug induced apoptosis and CPT1C, involved in mitochondrial dysfunction. Ingenuity pathway analyses revealed enrichment of genes involved in the canonical pathway AMPK signaling including CPT1C, CKM and PIK3CG. AMPK signaling stimulates signaling pathways that replenish cellular ATP supplies in response to low glucose, hypoxia, ischemia, or heat shock, which may be triggered in response of myeloma cells to bortezomib. Significant SNPs (permutated P Conclusion. We identified molecular factors which are associated with BiPN in newly diagnosed multiple myeloma patients. First, apoptosis genes contribute to early BiPN, whereas genes involved in inflammatory pathways and DNA repair contribute to the development of late BiPN, indicating that distinct genetic factors are involved in the development of early and late onset BiPN. Second, myeloma-related factors and host genetic background interactively contribute to the development of BiPN. Comparison between BiPN and ViPN learned that genetic factors involved in the development of PN are involved in different molecular mechanisms. This investigation strongly suggests an interaction between myeloma-related factors and host genetic background in the development of bortezomib induced peripheral neuropathy. Disclosures: Goldschmidt: Celgene: Membership on an entity's Board of Directors or advisory committees; Ortho Biotec: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Ortho Biotec: Research Funding; Chugai Pharma: Research Funding; Amgen: Research Funding. Sonneveld:Ortho Biotech: Consultancy; Ortho Biotech: Research Funding; International Myeloma Foundation: Research Funding.

Background: Multiple myeloma (MM) remains an incurable malignancy, but new treatment modalities can achieve durable remissions in most cases. Remission is generally regarded as a window of opportunity for active immunotherapy, aimed at eradicating residual disease. For immunotherapy, and vaccination in particular, the expression of cancer testis antigens (CTAs) in MM has emerged as a key target that is essentially tumor-specific. These CTAs are expressed at disease presentation, many confirmed also at the protein level. However, the question has remained whether treatment might critically alter the expression profile of CTAs. To address this, we have examined the expression levels of a large panel of known CTAs using gene expression profiles (GEPs) from patient cohorts in clinical trials at defined stages: at disease presentation in HOVON-65 and post-treatment in the APEX, SUMMIT and CREST trials. Methods and results: The APEX, SUMMIT and CREST trials have been described by Mulligan et al. (Blood, 109, 3177; 2007) and data consist of GEPs obtained from 264 patients with relapse following prior therapies (median number of therapies, 3; min-max, 1–14). In the HOVON-65 study, GEPs of 204 previously untreated myeloma cases were obtained. For comparison of both studies, original raw data files (CEL-files) were obtained and analyzed using Partek software. After normalization and merging, the expression of 62 CTA genes and gene clusters was evaluated. 63 probe sets were used, of which 51 correspond to 50 unique genes and 12 correspond to clusters of cancer antigen genes. Normalized expression levels for 24/62 genes/gene clusters were well above cut-off, and for remainder (38/62) were generally low with medians below 30. High median expression values, in the top 10% of CTA expression values, were found for SSX2, MAGE-A3 and MAGE-C1. Genes in the bottom 10% include MAGE-B1 and SPACA3. Notably, of 62, the fold change in expression level before and after treatment was at most 1.5 in any of the genes studied, indicating that the expression of the majority of CTAs is unchanged by treatment. For 8 genes/gene clusters, significantly decreased expression was found in relapsed cases compared to untreated MM, including GAGE3 and a gene cluster containing the GAGE1 gene. Conclusion: These clinical trial data indicate that targeting CTAs with immunotherapy during first remission or after relapse of MM remains a viable option.

Multiple Myeloma (MM) is characterized by the presence of a monoclonal protein, immunodeficiency, anemia, renal failure and bone lesions. New agents like Bortezomib (Bor) and Thalidomide (Thal) have shown efficacy in 40% of patients with relapsed/refractory MM, and up to 75% in first-line treatment. Classical prognostic classifications such as serum b2-microglobulin, albumin and chromosomal aberrations, have insufficient predictive power in estimating long-term outcome with these targeted agents. We have performed gene expression profiling (GEP) in newly diagnosed MM patients who were included in a large multicenter, prospective phase III trial (HOVON65) comparing Bor with standard induction prior to high dose therapy (HDT). The aim of this profiling was to gain new insights in the pathogenesis of MM and to design a prognostic index for treatment based on molecular profiling. In 258 patients, CD138 magnetic cell selected (MACS) myeloma plasma cells (PC) obtained at diagnosis with PC purity > 80% were used for RNA extraction and applied to the Affymetrix GeneChip U133 plus 2.0 arrays. Data from the gene expression arrays were pre-processed using GCRMA (Bioconductor). Unsupervised gene clustering (Omniviz) using a correlation visualisation matrix could determine the clusters based on the top variably expressed genes, and differential gene expression within these clusters could be determined (BRB-array tools, p

Background: Bortezomib (Bor), a proteasome inhibitor, and Thalidomide (Thal), an anti-angiogenic and immunomodulatory drug, have a remarkable effect in patients with relapsed or refractory MM with 30–40% response rates. In newly diagnosed patients the response rates vary from 70–85%. However, 15–30% of newly diagnosed patients do not respond to Bor or Thal. Secondly, 30% of the patients treated with these novel agents have to stop prematurely because of intolerable side effects, such as polyneuropathy, thrombocytopenia, thrombosis and gastro-intestinal symptoms. Aim: To gain new insights regarding the mechanisms of drug response and toxicity associated with these agents, we have embarked on a prospective study to analyze gene expression profiles (GEP) of myeloma specific genes in plasma cells purified from bone marrow from myeloma patients at diagnosis who have been treated with these novel agents in order to learn which genes govern outcome upon treatment with Bor and Thal. Methods: GEP of CD138 magnetic cell selected (MACS) myeloma plasma cells was performed using Affymetrix GeneChip Human Genome U133 plus 2.0 arrays. This program has been initiated in a large multicenter, prospective, randomized phase III trial, comparing Bor in combination with Adriamycin, Dex (PAD, arm A) followed by high dose therapy with stem cell rescue and maintenance therapy with Bor vs. Vincristine, Adriamycin and Dex (VAD, arm B) followed by high dose therapy with stem cell rescue and maintenance therapy with Thalidomide (HOVON65/GMMG-HD4). This cooperative trial in the Netherlands and Germany has started in April 2005 and has included 600 patients. Gene arrays were analyzed using correlation analysis in Omniviz. Differentially expressed genes in the different groups and in Bor responders were determined using a t-test with adjusted p-value (p Results: Based on correlated GEPs we divided myeloma patients into 10 clusters. We determined differentially expressed genes in the different clusters and correlated the clusters with chromosomal aberrations like 13q loss, 9 and 11 gain and translocations. Three clusters showed high expression of MMSET/FGFR3, MAF downstream targets and CCND1, respectively. Conclusion: unsupervised cluster analysis led to the subdivision of myeloma patients into clusters, each with a specific gene expression signature. We determined differentially expressed genes in the different clusters and could confirm 3 subgroups (MMSET/FGFR3, MAF/MAFB, and a group with high CCND1 expression) as have been published before.

Introduction: Clinical development of bortezomib in multiple myeloma (MM) included pharmacogenomic gene expression profiling (GEP) of pre-treatment tumor biopsies in order to evaluate the feasibility of developing predictive classifiers in prospective clinical trials and to better define the biological pathways related to drug sensitivity. By partitioning the samples into train (n=101) and test (n=80) datasets, statistically significant classifiers of response and survival were identified and then validated [Mulligan G, et al: Blood. 2007; 109:3177–88]. Here we describe specific genes and biological pathways associated with bortezomib efficacy in relapsed MM. Methods: Using tumor GEP data from 188 patients treated with single-agent bortezomib we identified genes associated with overall survival (OS), as well as genes associated with response (R) or progressive disease (PD) after bortezomib therapy. These clinical endpoints were also analyzed with biological pathway algorithms including GSEA [Subramanian A, et al: Proc Natl Acad Sci2005; 102:15545–50] Ingenuity Pathway Analysis and Gene Ontology/GATHER. These results were then compared to GEP data from a patient subset (n=76) treated with single-agent dexamethasone and also cell lines selected for differential sensitivity to bortezomib. Results: A comparison of R and PD highlighted numerous differentially expressed genes; approximately 200 were over-expressed in R and 500 were over-expressed in PD (t-test Conclusions: This study highlights the diversity of biological pathways expressed in MM and the utility of clinical genomics to associate pathways with activity of single-agent bortezomib.

Multiple myeloma is a disease of the antibody producing plasma cells in the bone marrow. It has been characterized by frequent genomic alterations including gains and losses of chromosomes. Some of these alterations result in poor clinical prognosis. Bortezomib, a first in class proteasome inhibitor, is approved for the treatment of relapsed multiple myeloma. To better understand how the genome wide changes observed in myeloma relate to prognosis and treatment response, we have used single nucleotide polymorphism (SNP) array technology to assess genotypes and DNA copy number at up to 100,000 genomic loci. DNA from 147 bone marrow tumor biopsies collected in multi-center phase II and III clinical trials of relapsed multiple myeloma patients prior to treatment with Bortezomib were hybridized on SNP arrays to assess genomic aberrations. Commonly seen genomic alterations in myeloma were observed, including deletions of chromosome 13 (37%), 1p (25%), 6q (23%), and amplifications on 1q (35%). We found that 35% of this relapsed myeloma population exhibited a hyperdiploid genome characterized by gains of chromosomes 3, 5, 7, 9, 11, 15, and 19. Other notable genomic deletions included 17p (22%), 8p (27%) and 10p (16%). A correlation of response to bortezomib therapy in patients with differential gains and losses at the chromosomal level is ongoing. Consistent with previous reports, response to bortezomib was observed in patients with poor prognostic chr 13 deletions. A more in-depth analysis of specific loci associated with clinical outcome will be discussed. In summary, this data will help further define genomic aberrations in multiple myeloma and their association with treatment outcome.

Consolidation treatment with high dose chemotherapy in combination with an autologous peripheral blood stem celll transplant. is widely used in patients with high risk non-Hodgkin lymphoma (NHL). Also this treatment has its place in patients with relapsed intermediate lymphoma. Earlier studies in patients with breast cancer or multiple myeloma showed evidence for (minimal) tumour contamination in the graft that might lead to the occurence of relapse. For patients with NHL this is less clear. For the present analysis 60 patients (pts) were included: 18 pts with primary high risk NHL, 6 patients with mantle cell lymphoma, and 36 pts with primary refractory or relapsed intermediate NHL. Patients with high risk NHL were treated with induction chemotherapy according to the Hovon-27 or Hovon-40 protocol(www.hovon.nl). Two patients (1 pt with T-Lymphoblastair lymphoma, 1 pt with Burkitt Lymphoma ) received intensive induction chemotherapy according to our leukemia protocols. Stem cells were collected as early as possible, provided the peripheral blood and bone marrow showed no histological evidence of NHL and < 20% lymfocytes. In the patients with mantle cell lymphoma stem cells were collected during the induction chemotherapy (Hovon-45 protocol:www.hovon.nl), irrespective of their presence in the bone marrow. The patients with primary refractory or relapsed intermediate NHL received reinduction chemotherapy with DHAP (Dexamethason, Cytarabin, Cisplatin) or EMP (Etopside, Mitoxantrone, Prednisone). After two or three courses peripheral blood stem cells were mobilised with G-CSF (Neupogen, Amgen) 10 μg/kg sc daily starting day 5 and harvested for autologous stem cell transplant. Before the start of mobilisation patients were required to be responsive to the induction chemotherapy and to have a bone marrow without histological and immunological detectable tumour cells. In all patients a sample of the first day stem cell collection was analyzed with the use of three or four colour Flowcytometry. The sensitivity of the assay was 1/ 104–105 lymphoma cells. Only in 3 pts tumour cells were found at a level > 0.05 %. Interestingly two patients had a primary diagnosis of diffuse large B-cell lymphoma T-cell/ histiocyte rich variant. Both pts relapsed: one within 6 months and the other one within 12 months.The third patient suffered from a anaplastic large cell T-cell lymphoma and relapsed after 15 months. In all other patients no lymphoma cells were detectable in the stemcell harvest at a minimum level of