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Supplementary Table from Safety and Efficacy of Combination Maintenance Therapy with Ixazomib and Lenalidomide in Patients with Posttransplant Myeloma

Supplementary Figure from Safety and Efficacy of Combination Maintenance Therapy with Ixazomib and Lenalidomide in Patients with Posttransplant Myeloma

Purpose:In this study, the addition of ixazomib to lenalidomide maintenance post-autologous stem cell transplant (ASCT) in 64 patients with newly diagnosed multiple myeloma was evaluated on the basis of the observed benefit of lenalidomide-only maintenance in prior studies.Patients and Methods:Patients were started on maintenance therapy with lenalidomide and ixazomib within 60–180 days of stem cell infusion.Results:Response rates deepened over time from baseline post-ASCT for 39 patients. The complete response (CR)/stringent CR rate was 43% and median overall survival was not reached with a median follow-up of 62 months (range, 25–82 months). Median PFS (mPFS) for all patients was 73 months and has not been reached for those with International Staging System (ISS) stage 1 disease. mPFS in 9 patients who had ISS stage 3 disease and 14 patients who had high-risk cytogenetics was 34 and 25 months, respectively. Twenty-two patients had progressive disease, while 19 patients continue to receive dual maintenance. The most common grade 3/4 adverse events included neutropenia, leukopenia, thrombocytopenia, lung infections, diarrhea, and maculopapular rash. Second primary malignancies occurred in 9 patients. Toxicity led to dose reductions in ixazomib and lenalidomide in 20 and 31 patients, respectively. Discontinuation of ixazomib due to toxicity occurred in 4 patients. Grade 1/2 neuropathy occurred in 22 patients and led to reduction or discontinuation of ixazomib in 2 patients.Conclusions:The addition of ixazomib to lenalidomide maintenance demonstrated a better than expected PFS compared with historical data using lenalidomide alone and was safe and tolerable.

Purpose: In this study, the addition of ixazomib to lenalidomide maintenance post-autologous stem cell transplant (ASCT) in 64 patients with newly diagnosed multiple myeloma was evaluated on the basis of the observed benefit of lenalidomide-only maintenance in prior studies. Patients and Methods: Patients were started on maintenance therapy with lenalidomide and ixazomib within 60–180 days of stem cell infusion. Results: Response rates deepened over time from baseline post-ASCT for 39 patients. The complete response (CR)/stringent CR rate was 43% and median overall survival was not reached with a median follow-up of 62 months (range, 25–82 months). Median PFS (mPFS) for all patients was 73 months and has not been reached for those with International Staging System (ISS) stage 1 disease. mPFS in 9 patients who had ISS stage 3 disease and 14 patients who had high-risk cytogenetics was 34 and 25 months, respectively. Twenty-two patients had progressive disease, while 19 patients continue to receive dual maintenance. The most common grade 3/4 adverse events included neutropenia, leukopenia, thrombocytopenia, lung infections, diarrhea, and maculopapular rash. Second primary malignancies occurred in 9 patients. Toxicity led to dose reductions in ixazomib and lenalidomide in 20 and 31 patients, respectively. Discontinuation of ixazomib due to toxicity occurred in 4 patients. Grade 1/2 neuropathy occurred in 22 patients and led to reduction or discontinuation of ixazomib in 2 patients. Conclusions: The addition of ixazomib to lenalidomide maintenance demonstrated a better than expected PFS compared with historical data using lenalidomide alone and was safe and tolerable.

Backrground: Several randomized controlled clinical trials have demonstrated improved outcomes for newly diagnosed multiple myeloma (NDMM) patients who were treated with lenalidomide as maintenance therapy after autologous stem cell transplant (ASCT). Proteasome inhibitors have demonstrated clinical benefit in myeloma patients when used as part of induction and maintenance regimens, and the combination of proteasome inhibitors and lenalidomide in induction regimens has produced strong clinical responses. In this study, the addition of ixazomib to lenalidomide maintenance post-ASCT in NDMM patients was evaluated. Methods: Patients (n=64) were started on maintenance therapy with lenalidomide and ixazomib within 60-180 days of stem cell infusion. Each cycle was defined as 28 days with lenalidomide starting at 10 mg/day orally for 28 days with the option to increase the dose to 15 mg after 3 cycles. Ixazomib was provided at 3 mg (n=48 patients) or 4 mg (n=16 patients) orally on days 1, 8, and 15 of each 28-day cycle. However, ixazomib dose was reduced to 3 mg in all patients based on toxicity observed in other clinical trials of ixazomib at that time. The primary endpoint measured was progression-free survival (PFS), which was defined as the time between ASCT and disease progression or death, whichever occurred first. Results: A total of 64 patients were enrolled on this study between December 4, 2012, and May 13, 2015. Of these patients, 41 (64.06%) were 60 years of age or older and 42 (65.63%) were male. Fourteen patients had high-risk cytogenetic features (+1q21, Del17p, t(14:16), t(4:14)), 50 patients had standard cytogenetic risk features (t(11:14), t(6:14), hyperdiploidy, normal) and 9 patients had International Staging System stage 3 disease. Median PFS (mPFS) for all patients was 73.3 months and has not been reached for those with ISS stage 1 disease. mPFS for ISS Stage 3 disease and high-risk cytogenetic subgroups was 33.8 and 25.4 months, respectively. Twenty-two patients had progressive disease, while 21 patients continue to receive dual maintenance. Response rates deepened over time from baseline post-ASCT for 39 patients. The complete response (CR)/stringent CR rate was 42.9% and median overall survival was not reached with a median follow-up of 62 months (range 25.4 - 82.1 months). Thirty-one patients (48%) had improvement from their baseline response after maintenance therapy: 6 patients improved from PR to VGPR; 7 from PR to stringent CR (sCR)/CR; 16 from VGPR to sCR/CR; 1 from SD to CR; and 1 patient improved from SD to VGPR. The median time to response in the 31 patients with improved response to maintenance therapy was 10.9 months (range, 0.9 to 51.3 months). Minimal residual disease (MRD) was evaluated by multicolor flow cytometry (10^-5) in 21 patients by bone marrow biopsy; 8 patients were MRD-positive. The most common grade 3/4 adverse events (AEs) included neutropenia (46.9%), leukopenia (20.3%), thrombocytopenia (15.6%), lung infections (26.6%), diarrhea and maculopapular rash (12.5% each). Secondary primary malignancies occurred in 9 patients; these included squamous cell carcinoma of the skin (n=4), basal cell carcinoma of the skin (n=1), squamous cell carcinoma and basal cell carcinoma of the skin (n=1), hepatocellular carcinoma (n=1), melanoma (n=1) and leukemia (n=1). AEs led to dose reductions in ixazomib and lenalidomide in 20 and 31 patients, respectively. Discontinuation of ixazomib due to AEs occurred in 4 patients. Grade 1/2 neuropathy occurred in 22 patients and led to reduction or discontinuation of ixazomib in 2 patients. Conclusion: Addition of ixazomib to lenalidomide maintenance in myeloma patients demonstrated a better than expected PFS compared with what has been reported in studies of lenalidomide alone, and was both safe and tolerable. These results indicate a significant clinical benefit, especially for standard risk patients. Figure 1 Figure 1. Disclosures Patel: Oncopeptides: Consultancy; Pfizer: Consultancy; Janssen: Consultancy, Research Funding; BMS Celgene: Consultancy, Research Funding. Shah: Karyopharm Therapeutics Inc.: Current Employment, Current equity holder in publicly-traded company. Lee: GlaxoSmithKline: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy; Celgene: Consultancy; Regeneron: Research Funding; Takeda Pharmaceuticals: Consultancy, Research Funding; Oncopetides: Consultancy; Amgen: Consultancy, Research Funding; Karyopharm: Consultancy; Legend Biotech: Consultancy; Sanofi: Consultancy; Janssen: Consultancy, Research Funding; Genentech: Consultancy. Thomas: BeiGene: Membership on an entity's Board of Directors or advisory committees; BMS: Research Funding; Ascentage Pharma: Research Funding; X4 Pharma: Research Funding; Genentech: Research Funding; Acerta Pharma: Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees. Qazilbash: NexImmune: Research Funding; Angiocrine: Research Funding; Amgen: Research Funding; Bristol-Myers Squibb: Other: Advisory Board; Oncopeptides: Other: Advisory Board; Janssen: Research Funding; Biolline: Research Funding. Orlowski: Amgen, Inc., BioTheryX, Inc., Bristol-Myers Squibb, Celgene, EcoR1 Capital LLC, Genzyme, GSK Biologicals, Janssen Biotech, Karyopharm Therapeutics, Inc., Neoleukin Corporation, Oncopeptides AB, Regeneron Pharmaceuticals, Inc., Sanofi-Aventis, and Takeda P: Consultancy, Honoraria; Asylia Therapeutics, Inc., BioTheryX, Inc., and Heidelberg Pharma, AG.: Other: Laboratory research funding; CARsgen Therapeutics, Celgene, Exelixis, Janssen Biotech, Sanofi-Aventis, Takeda Pharmaceuticals North America, Inc.: Other: Clinical research funding; Asylia Therapeutics, Inc.: Current holder of individual stocks in a privately-held company, Patents & Royalties; Amgen, Inc., BioTheryX, Inc., Bristol-Myers Squibb, Celgene, Forma Therapeutics, Genzyme, GSK Biologicals, Janssen Biotech, Juno Therapeutics, Karyopharm Therapeutics, Inc., Kite Pharma, Neoleukin Corporation, Oncopeptides AB, Regeneron Pharmaceuticals, I: Membership on an entity's Board of Directors or advisory committees.

Background: Lenalidomide (LEN) monotherapy has been effective in extending progression free survival (PFS) after AuSCT in pts with MM. Elotuzumab (ELO), a humanized IgG1 immunostimulatory monoclonal antibody against signaling lymphocytic activation molecule F7 (SLAM F7), is FDA approved in combination with LEN and dexamethasone (DEX) for treatment of MM pts who have received 1-3 prior therapies. We report updated results of this phase 2 trial evaluating the efficacy and safety of adding ELO to LEN as maintenance therapy post- AuSCT. Patients and Methods: Between 4/15/2015-1/27/2016, 27 evaluable pts were treated on 28 day cycles with ELO, 10 mg/kg iv weekly for cycles 1-2, q2weeks for cycles 3-6, then 20 mg/kg once monthly for cycles 7+. Pts enrolled after 1/28/2016 (n=73 pts) have received ELO, 10 mg/kg IV weekly for cycles 1-2, and 20 mg/kg on day 1 from cycle 3 until disease progression (PD). LEN has been dosed at 10 mg/day for cycles 1-3, with a dose increase to 15 mg/day at physician discretion starting with cycle 4, in the absence of non-hematologic toxicity > grade 1 and significant cytopenias (ANC < 1000/mL, platelet count < 100,000/ml). For the 1st 8 weeks, pts The study's primary endpoint is PFS, defined as time from AuSCT to PD or death (whichever occurs first), or censored at date of last contact. Secondary objectives are best response, OS, incidence of second primary malignancies (SPMs) and adverse event (AE) profile. Total enrollment of 100 evaluable pts was completed on 6/5/2019. Patients are followed until death, withdrawal of consent or removal from study. Eligible pts received ≤2 lines of induction therapy, and were 60-210 days post-AuSCT. Results: Pts (n=100) have been treated for a median of 27.5 cycles (4-67). At study entry, 37 (37%) had complete response (CR), 40 (40%) very good partial response (VGPR), 22 (22%) partial response (PR) and 1 (1%) minor response (MR). Best response achieved to date on study is CR in 61 pts (61%), VGPR in 29 pts (29%) and PR in 10 pts (10%). Median time for conversion to CR on study is 1 month. Of pts in CR and tested for minimal residual disease (MRD) to date, 42/48 are negative (flow cytometry on ≥ 2 x106 cells). Eleven of 42 have converted from VGPR to MRD negative CR while on study. With a median follow up of 41 months, 90% of pts (n=90) remain alive. Eighteen pts have had PD; of these, 10 had high-risk cytogenetics. Three died of PD while receiving salvage therapy, 1 of pneumonia, 4 of second malignancies and 1 of unknown cause at another facility. One additional pt died on study in VGPR, after developing acute cerebral encephalopathy with refractory status epilepticus of unclear etiology. Estimated 4 year PFS is 75%. High-risk cytogenetics (n =31) adversely affected PFS (p=0.01); 14/31 pts remain on study. Of 23 pts transitioned to another therapy, median 2nd PFS has not been reached. Grade 3-4 Hematologic AEs (no. of pts/102 pts) were: neutropenia 32% (33), febrile neutropenia 15% (15), thrombocytopenia 7% (7), and anemia 10% (10). Grade 3-4 non-Hematologic AEs (no. of pts): hypophosphatemia 29% (30), respiratory infections 21% (21), diarrhea 15% (15), fatigue 12% (12), peripheral neuropathy 8% (8), other infections 7% (7), myalgias 5% (5), dyspnea 5% (5). SPMs include cutaneous basal and squamous cell carcinomas (8), AML (1), B-cell ALL (1), t-MDS (4), osteosarcoma (1), intra-epidermal adenocarcinoma of the neck (1), mucinous appendiceal neoplasm (1), mucinous epidermoid carcinoma of parotid (1), prostate cancer (1). Renal cell carcinoma was diagnosed in 1 pt, 15 months after removal from study for PD. Conclusions: Lenalidomide-elotuzumab is a well-tolerated maintenance therapy on which 38% of pts have had improvement in quality of response while on therapy, including 27% who converted to CR. SPM rates seem consistent with those observed in CALGB 100104 and IFM 2005-02 trials of lenalidomide alone. Longer follow up is required to determine how median PFS and OS will compare with those from lenalidomide monotherapy trials, and how SPM rates will continue to evolve. Table 1 Disclosures Thomas: X4 Pharma: Research Funding; Ascentage: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Research Funding; Xencor: Research Funding; Pharmacyclics: Other: Advisory Boards; Genentech: Research Funding. Shah:Karyopharm: Current Employment, Current equity holder in publicly-traded company. Lee:Regeneron: Research Funding; Daiichi Sankyo: Research Funding; Sanofi: Consultancy; GlaxoSmithKline: Consultancy, Research Funding; Genentech: Consultancy; Takeda: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Genentech: Consultancy. Manasanch:JW Pharma: Research Funding; Merck: Research Funding; Quest Diagnostics: Research Funding; Takeda: Honoraria; BMS: Honoraria; Glaxo Smith Kline: Honoraria; Adaptive Biotechnologies: Honoraria; Novartis: Research Funding; Sanofi: Honoraria, Research Funding. Patel:Oncopeptides: Consultancy; Takeda: Consultancy, Research Funding; Cellectis: Research Funding; Bristol Myers Squibb: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Nektar: Consultancy, Research Funding; Precision Biosciences: Research Funding; Poseida: Research Funding. Kaufman:Bristol Myers Squibb: Research Funding; Karyopharm: Honoraria; Janssen: Research Funding. Iyer:Trillium: Research Funding; Daiichi Sankyo: Consultancy; Legend Biotech: Consultancy; Merck: Research Funding; Rhizen: Research Funding; Seattle Genetics, Inc.: Research Funding; Target Oncology: Honoraria; Afffimed: Research Funding; CRISPR: Research Funding; Spectrum: Research Funding; Curio Biosciences: Honoraria. Qazilbash:Angiocrine: Research Funding; Bioclinica: Consultancy; Janssen: Research Funding; Bioline: Research Funding; Amgen: Research Funding. Bashir:Amgen: Other: Advisory Board; Purdue: Other: Advisory Board; Takeda: Other: Advisory Board, Research Funding; Acrotech: Research Funding; StemLine: Research Funding; Celgene: Research Funding; KITE: Other: Advisory Board. Orlowski: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; 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. OffLabel Disclosure: Elotuzumab (ELO), a humanized IgG1 immunostimulatory monoclonal antibody against SLAM F7. It is FDA approved in combination with Lenalidomide and dexamethasone (DEX) for treatment of MM pts who have received 1-3 prior therapies. This is a phase 2 trial evaluating the efficacy and safety of adding ELO to LEN as maintenance therapy post-autologous stem cell transplant.

Background: Lenalidomide (LEN) monotherapy has been effective in extending progression free survival (PFS) after myeloablative AuSCT in pts with MM. Elotuzumab (ELO), a humanized IgG1 immunostimulatory monoclonal antibody against signaling lymphocytic activation molecule F7 (SLAM F7), is FDA approved in combination with LEN and dexamethasone (DEX) for treatment of MM pts who have received 1-3 prior therapies. The objective of this phase 2 trial is to evaluate the efficacy and safety of adding ELO to LEN as maintenance therapy post-myeloablative AuSCT. We report updated results of the primary (PFS) and secondary (overall survival [OS] and toxicity) endpoints. Patients and Methods: Between 4/15/2015-1/27/2016, 27 evaluable pts were treated on 28 day cycles with ELO, 10 mg/kg iv weekly for cycles 1-2, q2weeks for cycles 3-6, then 20 mg/kg once monthly for cycles 7+. Pts enrolled after 1/28/2016 (n=57 pts) have received ELO, 10 mg/kg IV weekly for cycles 1-2, and 20 mg/kg on day 1 from cycle 3 until disease progression (PD). LEN has been dosed at 10 mg/day for cycles 1-3, with a dose increase to 15 mg/day at physician discretion starting with cycle 4, in the absence of non-hematologic toxicity > grade 1 and significant cytopenias (ANC < 1000/mL, platelet count < 100,000/ml). For the 1st 8 weeks, pts The study's primary endpoint is PFS, defined as time from AuSCT to PD or death (whichever occurs first), or time of last contact. Secondary objectives are best response, OS, incidence of second primary malignancies (SPMs) and adverse event (AE) profile. Total enrollment of 100 pts is planned. Patients are followed until death, withdrawal of consent or removal from study. Eligible pts received ≤2 lines of induction therapy, and are 60-210 days post-AuSCT. Results: Pts (n=84) have been treated for a median of 16 cycles (2-43). At study entry, 27 (32%) had complete response (CR), 36 (43%) had very good partial remission (VGPR), 20 (24%) had partial remission (PR) and 1 (2%) had minor remission (MR). Best response achieved to date on study is CR in 44 pts (52%), VGPR in 31 pts (37%) and PR in 9 pts (11%). For those who have converted to CR on study, median time to CR was 2 months. Of 22 pts in CR who have been tested for minimal residual disease (MRD) to date, 20 are negative by flow cytometry (minimum of 2 million cells evaluated). Three of 20 have converted from VGPR to MRD negativity while on study. With a median follow up of 23 months, 96% of pts (n=81) remain alive. Ten pts have had PD; of these, 6 had high risk cytogenetics. Two died of PD while receiving salvage therapy. One additional pt died on study in VGPR, after developing acute cerebral encephalopathy with refractory status epilepticus of unclear etiology. Four pts withdrew for personal reasons, 4 were removed at physician discretion (prolonged cytopenias [1], drug rash [1], worsening memory impairment [1], therapy related myelodysplastic syndrome (t-MDS) [1]), and 2 lost insurance coverage. Estimated 3 year PFS is 81%. High risk cytogenetics adversely affected PFS (p=0.02). Grade 3-4 Hematologic AEs (no. of pts) were: neutropenia 32% (27), febrile neutropenia 15% (13), thrombocytopenia 8% (7), and anemia 7% (6). Grade 3-4 non-Hematologic AEs (no. of pts): respiratory infections 17% (15), diarrhea 14% (12), fatigue 13% (11), other infections 8% (7), peripheral neuropathy 7% (6), myalgias 6% (5), nausea/vomiting 4% (3), dizziness 2% (2), memory impairment 2% (2), maculopapular rash 2% (2), edema 1% (1). SPMs include intra-epidermal adenocarcinoma of the neck (1), mucinous appendiceal neoplasm (1), t-MDS (1), prostate cancer (1), and melanoma (1). Renal cell carcinoma was diagnosed in 1 pt, 15 months after removal from study for PD. Conclusions: Lenalidomide-elotuzumab is a well-tolerated maintenance therapy during which 33% of 84 pts had improvement in quality of response while on therapy, including 20% who converted to CR. The number of pts experiencing improvement may be underestimated due to ELO interference with paraprotein measurement on electrophoretic studies. Additional follow up is required to determine if the improved quality of responses translate into improvements in PFS and OS. Available data supports conduct of a Phase 3 trial. Disclosures Thomas: Array Pharma: Research Funding; Amgen Inc: Research Funding; Bristol Myers Squibb Inc.: Research Funding; Acerta Pharma: Research Funding; Celgene: Research Funding. Shah:Karyopharm Therapeutics: Employment. Lee:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies Corporation: Consultancy; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Chugai Biopharmaceuticals: Consultancy; Takeda Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kite Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees. Patel:Abbvie: Research Funding; Celgene: Research Funding; Takeda: Research Funding; Poseida Therapeutics, Inc.: Research Funding.

Background: Lenalidomide (LEN) monotherapy has been effective in extending progression free survival (PFS) and after myeloablative AuSCT in patients (pts) with multiple myeloma (MM) (Attal et al. NEJM 2012, McCarthy et al. NEJM 2012,). Elotuzumab (ELO), a humanized IgG1 immunostimulatory monoclonal antibody against signaling lymphocytic activation molecule F7 (SLAMF7), is FDA approved in combination with LEN and dexamethasone (DEX) for treatment of pts with MM who have received 1-3 prior therapies. The objective of this phase 2 trial is to evaluate the efficacy and safety of adding ELO to LEN as maintenance therapy post-myeloablative AuSCT. We report preliminary results of the primary (PFS) and secondary (overall survival and toxicity) endpoints. Patients and Methods: Between 4/15/2015-1/27/2016, 28 evaluable pts were treated on 28 day cycles with ELO, 10 mg/kg iv weekly for cycles 1-2 and q2weeks for cycles 3-6, then 20 mg/kg once monthly for cycles 7+. Pts enrolled after 1/28/2016 (n=27 pts) have received ELO, 10 mg/kg IV weekly for cycles 1-2, and 20 mg/kg on day 1 from cycle 3 until progression. LEN has been dosed at 10 mg/day for cycles 1-3, with a dose increase to 15 mg/day at physician discretion starting with cycle 4, in the absence of non-hematologic toxicity > grade 1 and significant cytopenias (ANC < 1000/mL, platelet count < 100,000/ml). For the 1st 8 weeks, pts The primary endpoint of the study is PFS, defined as the time from AuSCT to clinical progression or death (whichever occurs first), or the time of last contact. Secondary objectives include best response, overall survival, incidence of second primary malignancies and adverse event (AE) profile. Total enrollment of 100 pts is planned. Pts will be followed for 48 months after the last patient is enrolled in the trial. Eligible pts had received no more than 2 lines of induction therapy, and were between 60-210 days post-AuSCT. Results: Patients (n=55) have been treated for a median of 14 cycles (2-30). At study entry, 13 pts (24%) had complete response (CR), 27 (49%) had very good partial remission (VGPR), 14 (25%) had partial remission (PR) and 1 (2%) had minor remission (MR). Best response achieved to date on study is CR in 28 pts (51%), VGPR in 23 pts (42%) and PR in 4 pts (7%). For those who have converted to CR on study, median time to CR has been 5 months. Of 14 pts in CR who have been tested for MRD while on study, 13 are negative by flow cytometry (minimum of 2 million cells evaluated; sensitivity 10 -4-10-5). Two of these 13 have converted from VGPR to MRD negativity at 4 and 14 months on study, respectively. With a median follow up of 21 months, 95% of pts (n=52) remain alive. Three pts (all with high risk disease) had disease progression at 4 (del 17p), 9 (t [4;14]), and 13 (gain 1q) months; of these, 2 have died of progressive disease while receiving salvage therapy. One patient, in VGPR, died on study after developing acute cerebral encephalopathy with refractory status epilepticus of unclear etiology. Two pts withdrew for logistical reasons; 2 have been taken off study per physician discretion (prolonged cytopenias (1), drug rash (1)). Grade 3-4 Hematologic AEs (no. of pts) were: neutropenia 35% (16), thrombocytopenia 9% (4), febrile neutropenia 7% (3), and anemia 7% (3). Grade 3-4 non-Hematologic AEs (no. of pts): diarrhea 17% (8), fatigue 17% (8), pneumonia 15% (7), other infections 15% (7), peripheral neuropathy 11% (5), myalgias 9% (4), nausea/vomiting 7% (3), maculopapular rash 4% (2), dizziness 4% (2), edema 2% (1), memory impairment 2% (1). Renal cell carcinoma was diagnosed in 1 patient, 15 months after removal from study for disease progression. Conclusions: Lenalidomide-elotuzumab is a well-tolerated maintenance therapy on which 44% of 55 pts have had improvement in quality of response while on therapy, including 28% who have converted to CR and 24% who have tested MRD negative. The number of pts who have experienced improvement on study may, in fact, be underestimated in this analysis due to elotuzumab interference with measurement on electrophoretic studies. Additional follow up is required to determine if the improved quality of responses translate into improvements in PFS and OS. Disclosures Thomas: Bristol Myers Squibb: Research Funding; Celgene: Research Funding. Shah: Kayopharm: Employment. Lee: Pimera Inc: Consultancy; Eutropics Pharmaceuticals: Research Funding; Adaptive: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Research Funding; Takeda: Consultancy; Celgene: Consultancy. Manasanch: merck: Research Funding; adaptive biotechnologies: Consultancy; sanofi: Research Funding; celgene: Consultancy; takeda: Consultancy; quest diagnostics: Research Funding. Patel: Juno: Consultancy; Celgene: Consultancy; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding. Orlowski: BioTheryX: Consultancy, Membership on an entity's Board of Directors or advisory committees.