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PD-1 blockade enhances the function of antitumor T cells and antibody-dependent, cell-mediated cytotoxicity (ADCC) of NK cells. In a single-center, open-label, phase 2 trial, we tested the combination of pembrolizumab, an anti-PD-1 monoclonal antibody, and rituximab, an anti-CD20 monoclonal antibody that induces ADCC, in 30 patients with follicular lymphoma (FL) with rituximab-sensitive disease who had relapsed after ≥1 prior therapy. Pembrolizumab was administered at 200 mg IV every 3 weeks for up to 16 cycles, and rituximab was given at 375 mg/m2 IV weekly for 4 weeks in cycle 1 only. The most common grade 3/4 adverse events (AEs) were liver enzyme abnormalities (3%), diarrhea (3%), nausea (3%), aseptic meningitis (3%), and pancreatitis (3%). Low-grade immune-related AEs were reported in 80% of patients, including diarrhea (43%), liver enzyme abnormalities (33%), thyroid dysfunction (27%), and rash (23%). Grade 3 or 4 immune-related AEs occurred in 13% of the patients. Treatment-related AEs led to discontinuation in 6 (20%) patients. The overall response rate (primary end point) was 67%, and the complete response (CR) rate was 50%. Median progression-free survival (PFS) was 12.6 months (95% confidence interval, 8.2-27.6), the 3-year overall survival rate was 97%, and 23% of patients were in remission at a median follow-up of 35 months. The presence of a high CD8+ T-effector score at baseline in the tumor was associated with induction of a CR and improved PFS. In this single-arm, phase 2 study, the combination of pembrolizumab and rituximab demonstrates favorable efficacy and safety profile in relapsed FL. This trial is registered at www.clinicaltrials.gov as #NCT02446457.

Richter syndrome (RS), an aggressive lymphoma occurring in the context of chronic lymphocytic leukaemia/small lymphocytic lymphoma, is associated with poor prognosis when treated with conventional immunochemotherapy, therefore, improved treatments are required. Immune checkpoint blockade has shown efficacy in some B-cell malignancies and modest responses in early clinical trials for RS. We investigated the immune checkpoint profile of RS as a basis to inform rational therapeutic investigations in RS. Formalin-fixed, paraffin-embedded biopsies of RS (n = 19), de novo diffuse large B-cell lymphoma (DLBCL; n = 58), transformed indolent lymphomas (follicular [tFL], n = 16; marginal zone [tMZL], n = 24) and non-transformed small lymphocytic lymphoma (SLL; n = 15) underwent gene expression profiling using the NanoString Human Immunology panel. Copy number assessment was performed using next-generation sequencing. Immunohistochemistry (IHC) for LAG3 and PD-1 was performed. LAG3 gene expression was higher in RS compared to DLBCL (P = 0·0002, log2FC 1·96), tFL (P

Primary and secondary central nervous system lymphomas (PCNSL/SCNSL) are aggressive rare malignancies with dismal outcomes. Encouraging data have emerged from Phase I/II clinical trials treating relapsed/refractory PCNSL/SCNSL with ibrutinib. We analysed 33 patients who received ibrutinib, alone or with other therapies, for PCNSL (n = 9) or SCNSL (n = 24). The objective response rate was 58% (complete response 55%). The median progression-free survival and overall survival for patients with PCNSL were both 3·1 months; for SCNSL, 10·2 and 11·5 months respectively. Only one invasive fungal infection was observed, despite concurrent or recent use of dexamethasone 8-16 mg daily in 14 patients (42%). Ibrutinib has encouraging activity in these aggressive malignancies.

Histologic transformation of indolent lymphomas account for 13% of de novo presentations of diffuse large B-cell lymphoma (DLBCL) [1]. Although historically associated with poor outcomes in compari...

Follicular lymphoma is the most common indolent non-Hodgkin lymphoma. Although median overall survival rates exceed 12 years with rituximab, follicular lymphoma remains largely incurable. The growing understanding of the molecular drivers of lymphomagenesis and the tumor microenvironment have led to novel therapies. Prognostic markers have identified a subset of patients with chemoresistant and/or refractory disease-associated poor outcomes. We identify the patients with follicular lymphoma in need of novel therapies, describe the drivers of lymphomagenesis and importance of the tumor microenvironment, and summarize the novel agents under investigation in relapsed/refractory and upfront follicular lymphoma.

High-dose chemotherapy (HDC) and autologous stem cell transplantation (ASCT) are used as consolidation in first remission (CR1) in some centres for untreated, transformed indolent B-cell lymphoma (Tr-iNHL) but the evidence base is weak. A total of 319 patients with untreated Tr-iNHL meeting prespecified transplant eligibility criteria [age

Central nervous system (CNS) relapses are an uncommon yet devastating complication of non-Hodgkin lymphomas. The identification of patients at high risk of secondary CNS relapse is therefore paramount. Retrospective data indicate prophylactic CNS-directed therapies may reduce the risk of CNS involvement; however, no consensus exists about dose, timing, or route of therapy. In addition, prophylaxis is not without risk of treatment-related complications and morbidity. Here, we present a series of case vignettes highlighting our approach to common dilemmas encountered in routine clinical practice. We review the method of assessing CNS relapse risk, factors that increase the likelihood of relapse including histologic subtype, MYC rearrangement, protein expression, and extranodal involvement, and review our clinical practice based on available evidence in administering CNS-directed prophylaxis.

e20020 Background: In the pivotal phase III study ECHELON-1, Brentuximab Vedotin (BV), doxorubicin, vinblastine, and dacarbazine (A+AVD) demonstrated superior efficacy but more hematological and neurological toxicity than bleomycin+AVD (ABVD) as therapy of advanced-stage untreated classic Hodgkin’s lymphoma (ucHL) (Straus et al Blood 2020). It is unknown if A+AVD in a real world setting shows the same efficacy and safety profile. Methods: After obtaining institutional research approval, we retrospectively reviewed the characteristics and outcomes of 41 stage III and IV ucHL patients treated per physician preference with A+AVD as standard of care between 3/2010 and 12/2019. Treatment consisted of 1.2 mg/kg of BV and standard dose AVD, intravenously on days 1 and 15 of each 28-day cycle for up to 6 cycles. All patients received support with granulocyte colony stimulating factor. Results: At time of treatment with A+AVD, median age was 38 (range 18-54 years) and IPS was 0-3 in 56% of patients. Overall, 95.1% of patients received 6 cycles of A+AVD, with a range of 3-6 cycles. During therapy, 19.5% of patients developed febrile neutropenia, 68.3% had at least one emergency department visit (median 2 visits, range 1-7), and 58.5% were hospitalized at least once (median hospital stay of 3 days, range 1-23). Furthermore, 4.9% of patients presented with grade ≥3 elevation of lipase, 4.9% grade ≥3 elevation of alanine aminotransferase, 9.8% deep vein thrombosis and 7.3% pulmonary embolism. Peripheral neuropathy (PN) occurred in 78% of patients, including grade ≥3 in 12.2%. Due to various toxicities, 22% of patients required at least one dose reduction of BV (median 5 reductions, range 2-7) and 46.3% had a least one dose omission of BV (median 4 omissions, range 1-10). At a median follow-up (FU) of 12.65 months (range: 5.91-85.97), 87.5% of patients had partial or complete improvement of their PN. The median delay of completion of 6 cycles of A+AVD was 8 days (range -1 to 35). The end-of-therapy PET/CT showed Deauville score of 1-3 in 85.3% of patients, 4 in 2.4% and 5 in 12.2%. However, only one patient relapsed 5 months after completion of 4 cycles of A+AVD and another relapsed 6 months after completion of 6 cycles. Both patients were still alive at last FU. The median PFS was not reached and 12-months PFS was 96.0% (95% confidence interval [CI], 88.6-100). Conclusions: In real-world experience, A+AVD is a highly effective treatment strategy for patients with advanced-stage ucHL. In light of its toxicity profile, strategies aimed at improving its safety are needed.

8021 Background: Transformation of untreated indolent B-cell lymphoma (Tr-iNHL) is associated with poor outcomes. Current practices are extrapolated from prospective studies of de novo large B-cell lymphoma (DLBCL) or small retrospective studies. High dose chemotherapy (HDC) and autologous stem cell transplantation (ASCT) is used as consolidation in first remission (CR1) in some centers but the evidence-base is weak. Methods: CLL/SLL, MCL as primary diseases and non-DLBCL transformations were excluded. Propensity score analysis (PSM) using the “greedy match” algorithm was used to match the baseline covariates to adjust for potential selection bias. Landmark analysis was performed with time zero at 3 months after completion of front line chemotherapy (FLC). Kaplan-Meier method and the Cox proportional hazards model were was used for time-to-event analysis including progression-free survival (PFS) and overall survival (OS). Results: 319 transplant eligible patients (age 45%, no severe lung disease, CR by PET or CT >3 months after FLC) who received >/= standard RCHOP intensity FLC were identified across three centers in Australia & US. 283 (89%) patients had follicular lymphoma, 30 (9%) marginal zone lymphoma, 6 (2%) other subtypes. 49 patients underwent HDC and ASCT in CR1, a matched cohort of 98 pts based on age, stage, HGBL-DH and ECOG PS at diagnosis was generated with a 1:2 ratio using PSM. After a median follow-up of 3.6 (min: 0.1, max: 18.3) years, ASCT was associated with significantly superior PFS on multivariable analysis (MVA) (HR 0.51, 0.27-0.98; P=0.043). Univariate analysis demonstrated a trend towards inferior OS in the ASCT cohort (HR 2.36; 0.87-6.42; P=0.092) with more deaths in the ASCT arm due to PD (8% v 4%). Of the 40 patients (41%) with relapsed disease in the non-ASCT cohort–15 patients underwent salvage HDC & ASCT with 7/15 (47%) ongoing CR; 10 patients underwent CAR-T therapy (5 relapse post ASCT, 4 refractory disease, 1 relapse post FLC) with 6/10 (60%) ongoing CR; 3 patients underwent allogeneic SCT (2 relapse post ASCT, 1 relapse post FLC) with 2/3 (67%) ongoing CR. Conclusions: Although ASCT in CR1 may improve initial duration of disease control in de novo Tr-iNHL, the impact on OS is less clear with effective salvage therapies in the CAR-T era.

8061 Background: Untreated transformed indolent lymphoma (unTIL) can present as a composite lymphoma (COM), 2 or more separate sites of disease with one site transformed (discordant; DIS) or following indolent lymphoma sequentially (SEQ). Current practices are guided by small retrospective studies or extrapolated from trials involving non-transformed lymphomas. Methods: 353 patients (pts) with biopsy-proven unTIL treated with curative chemoimmunotherapy between 01/2000 to 01/2019 were included (intention to treat). All indolent B-cell lymphomas (iNHL) were included except CLL/SLL. Patients with MCL and non-DLBCL transformation were excluded. Prior therapy for iNHL was not allowed except one line of non-chemotherapy-based therapy. Kaplan-Meier method was used for time-to-event analysis including progression-free (PFS) and overall survival (OS). Results: 252 (71%) pts presented with COM, 50 (14%) DIS and 51 (14%) SEQ lymphoma. The underlying iNHL was: 308 (87%) follicular lymphoma, 37 (10%) nodal MZL, 7 (2%) MALT lymphoma, and 1 (0.3%) WM. Frontline therapy (FLT) included: RCHOP for 271 (77%), DAEPOCHR for 60 (17%), clinical trial for 7 (2%), BR for 4 (1%), RHCVAD for 2 (1%), RCEOP for 2 (1%), radiation therapy for 2 (1%), RFND for (1%) 2, RCVP for 2 (1%), and rituximab only for 1 (0.3%). 9 (3%) pts had ASCT in first remission. 50 (15%) pts received maintenance rituximab (MR) with fewer cases of HGBL-DH compared to the non-MR cohort (0% v 10%). With a median follow-up of 3.4 years (range 0.1-19.1), 4-year PFS and OS rates were 59% and 88%. By univariate analysis (UVA) the underlying type of iNHL, cell-of-origin and choice of induction therapy (DAEPOCHR v RCHOP) were not associated with inferior outcomes. SEQ transformations were associated with inferior OS on UVA (P = 0.02) which was not significant on multivariable analysis (MVA) (P = 0.3). MVA identified ECOG PS > 1, B symptoms and HGBL-DH as independent prognostic factors for inferior PFS and OS. In patients who achieved PR or greater following FLT, MR was associated with improved PFS on MVA (HR 0.6, 95% CI 0.3-0.9, P = 0.04) without an OS benefit (P = 0.2). 39 (31%) pts relapsed with iNHL only (mPFS 2.4 yrs, 4-yr OS 94%) and 88 (69%) relapsed with transformed lymphoma (mPFS 1.1 yrs, 4-yr OS 69%) with no significant difference in pattern of relapse with MR (P = 0.2). Conclusions: The clinicopathologic features of unTIL are similar to those of de novo DLBCL. Escalation of therapy beyond R-CHOP may not be required in the absence of HGBL-DH. unTIL should be included in future clinical trials involving de novo DLBCL given the similar clinicopathologic features.

De novo diffuse large B-cell lymphoma (DLBCL) presenting with synchronous central nervous system (CNS) and systemic disease (synDLBCL) is not well described and is excluded from clinical trials. We performed a retrospective analysis of 80 synDLBCL patients treated across 10 Australian and UK centres. Of these patients, 96% had extranodal systemic disease. CNS-directed treatment with combination intravenous cytarabine and high-dose methotrexate ("CNS-intensive") (n = 38) was associated with favourable survival outcomes compared with "CNS-conservative" strategies such as intravenous high-dose methotrexate monotherapy, intrathecal therapy and/or radiotherapy (2-year progression-free survival [PFS] 50% vs. 31%, P = 0·006; 2-year overall survival [OS] 54% vs. 44%, P = 0·037). Outcomes were primarily dictated by the ability to control the CNS disease, with 2-year cumulative CNS relapse incidence of 42% and non-CNS relapse 21%. Two-year OS for CNS-relapse patients was 13% vs. 36% for non-CNS relapses (P = 0·02). Autologous stem cell transplantation as consolidation (n = 14) was not observed to improve survival in those patients who received CNS-intensive induction when matched for induction outcomes (2-year PFS 69% vs. 56%, P = 0·99; 2-year OS 66% vs. 56%, P = 0·98). Hyperfractionated or infusional systemic treatment did not improve survival compared to R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone) (2-year OS 49% for both groups). Our study suggests that adequate control of the CNS disease is paramount and is best achieved by intensive CNS-directed induction.

The application of molecular genomics and our understanding of its clinical implications in the diagnosis, prognostication and treatment of lymphoproliferative disorders has rapidly evolved over the past few years. Of particular importance are indolent B-cell malignancies where tumour cell survival and proliferation are commonly driven by mutations involving the B-cell receptor and downstream signalling pathways. In addition, the increasing number of novel therapies and targeted agents have provided clinicians with new therapeutic options with the aim of exploiting such mutations. In this case report, we highlight one such success story involving the diagnostic impact of the MYD88L265P mutation in Waldenstrom's macroglobulinemia (WM), its prognostic implications and effect on choice of therapy in the era of novel therapies.

Background: Patients with advanced indolent non-Hodgkin lymphoma (iNHL) can develop chemoresistance and most relapse following standard therapy. Although multiple treatment options exist, most are associated with short remission or intolerable side effects. Lenalidomide activates NK cells ± T cells and leads to in vivo expansion of immune effector cells in NHL models. The combination of rituximab and lenalidomide (R2) in relapsed iNHL is highly active and was recently approved. Obinutuzumab is a glycosylated type II anti-CD20 molecule with enhanced affinity for the FcγRIIIa receptors leading to improved ADCC. The primary objective of this phase I/II study was to determine the maximum tolerated dose (MTD), safety, and efficacy of lenalidomide and obinutuzumab in relapsed indolent lymphoma. Methods: Patients with relapsed small lymphocytic lymphoma (SLL), marginal zone, and follicular lymphoma (gr 1-3a) were eligible. Patients enrolled in three predefined dose cohorts of lenalidomide (10mg,15mg, 20mg) given on days 2-22 of a 28 day cycle. Obinutuzumab was given at a fixed dose (1000mg) IV on days 1,8,15 and 22 of cycle 1 and day 1 of subsequent cycles for 6 cycles. The combination was given for up to 12 cycles in responding pts. Antihistamines were given in pts who developed rash. Prophylactic growth factor was not allowed. In the absence of progression or toxicity, single agent obinutuzumab was continued every 2 months for maximum of 30 months on study. Traditional 3+3 dose escalation was used with dose limiting toxicities (DLT) assessed during cycle 1. Once the MTD was established, 60 additional patients were enrolled in the phase II portion of the study. Adverse events were graded using CTCAE version 4.03. Results: 66 pts were enrolled between May 2014 until March 2019, and all are eligible for safety and response assessment. No DLTs were observed in dose escalation, and 60 pts were enrolled in the phase II portion of the study at 20mg of lenalidomide daily. Histologies included follicular lymphoma (FL) n=57, marginal zone n=4, SLL n=5. The median age was 64 (36-81), with 2 (1-5) median prior lines of treatment. For 53% of pts, the combination represented the third or greater line of treatment. The overall response (OR) rate for all pts was 98% with 72% attaining a complete response (CR). Eighteen pts (27%) had a partial response, and stable disease was noted in 1 (2%). At a median follow up of 17 months, 14 pts have progressed, with an estimated 24mo progression-free survival (PFS) of 73% (57-83% 95% CI). The estimated 24 mo PFS for ≥ third line pts was 63%. Twenty five pts (38%) remain on treatment and 95% remain alive at last follow up. The most common grade ≥ 3 non-hematologic toxicities included fatigue (5 pts), rash (4 pts), and cough (3 pts). Grade ≥3 neutropenia and thrombocytopenia occurred in 11 (17%) and 7 (11%) pts respectively. Two pts stopped treatment due to adverse events, including 1 transient bradycardia and 1 grade 3 fatigue. Conclusion: The combination of 20 mg of lenalidomide and 1000mg obinutuzumab is safe and effective in patients with relapsed indolent lymphoma. Adverse events appeared similar to our prior experience with lenalidomide and rituximab and were generally well tolerated. Overall response rates were high, with many pts achieving prolonged remission, including pts who had relapsed after 2 or more lines of prior therapy. Validation studies in the frontline and salvage setting are ongoing. Disclosures Fowler: Celgene: 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, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals Corporation: Consultancy; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; ABBVIE: Membership on an entity's Board of Directors or advisory committees, Research Funding. Nastoupil:TG Therapeutics: Honoraria, Research Funding; Novartis: Honoraria; Janssen: Honoraria, Research Funding; Spectrum: Honoraria; Gilead: Honoraria; Genentech, Inc.: Honoraria, Research Funding; Bayer: Honoraria; Celgene: Honoraria, Research Funding. Westin:Novartis: Other: Advisory Board, Research Funding; Celgene: Other: Advisory Board, Research Funding; Juno: Other: Advisory Board; Janssen: Other: Advisory Board, Research Funding; Kite: Other: Advisory Board, Research Funding; Unum: Research Funding; MorphoSys: Other: Advisory Board; Genentech: Other: Advisory Board, Research Funding; Curis: Other: Advisory Board, Research Funding; 47 Inc: Research Funding. Neelapu:Precision Biosciences: Consultancy; Merck: Consultancy, Research Funding; Cellectis: Research Funding; Novartis: Consultancy; BMS: Research Funding; Karus: Research Funding; Acerta: Research Funding; Poseida: Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; Incyte: Consultancy; Celgene: Consultancy, Research Funding; Unum Therapeutics: Consultancy, Research Funding; Allogene: Consultancy; Pfizer: Consultancy; Cell Medica: Consultancy.

Background Approximately half of patients with relapsed or refractory (R/R) classical Hodgkin lymphoma (cHL) will relapse despite curative intent therapy with salvage chemotherapy (SC) and autologous stem cell transplantation (ASCT). Consolidative radiotherapy (cRT) is used to reduce the risk of local relapse in high risk patients. We aimed to examine the (i) impact of cRT on outcomes, (ii) role of positron-emission tomography computerised tomography (PET-CT) imaging in predicting outcomes, (iii) identify a subgroup most likely to benefit from cRT, (iv) assess patterns of relapse to understand the mechanisms of treatment failure and (v) propose a PET-CT based risk stratification model for relapse. Patients and Methods 104 patients with R/R cHL treated with curative intent SC and ASCT between January 2000 and May 2019 were retrospectively identified from two sites in Melbourne, Australia. Fifty-six patients (54%) received peri-transplant cRT. SC consisted of chemotherapy and/or immunotherapy of the clinician's choice followed by interim assessment by PET-CT imaging. Patients with a complete or partial metabolic response proceeded to ASCT. Disease status was routinely evaluated by physical examination and PET-CT imaging at time of disease relapse, at completion of salvage chemotherapy, and at three months following ASCT. A complete metabolic response on fluorodeoxyglucose (FDG) PET/CT was defined by Deauville Score ≤3 (uptake ≤ liver, PET negative) and compared to Deauville Score ≥4 (PET positive). Results With a median follow-up of 2.5 (range 0.2-15.2) years, the 2-year progression free survival (PFS) and overall survival (OS) rates were 68.3% and 83.6%, respectively. Inferior PFS was associated with advanced stage (III or IV) disease at relapse (AS-R) (53% vs 78%; P=0.004) and PET positivity after SC (51% vs 79%; P=0.005). Compared to PET negative patients after SC, 2-year PFS was significantly inferior in patients who were PET positive and did not receive cRT (38% vs 79%; P Conclusion One third of patients with relapsed/refractory cHL who received SC and ASCT subsequently relapsed within two years. cRT may abrogate the negative predictive value of a positive PET scan after SC, of which patients with LS-R are most likely to benefit. PET positive disease and residual mass ≥2cm after SC are associated with inferior PFS despite the use of cRT. Conversely, patients who are PET negative without residual tumor mass after SC have superior outcomes. cRT is associated with improved local disease control, yet approximately half of patients who relapse after cRT will still have in-field relapse, possibly warranting the evaluation of higher cRT doses. Therefore, we propose a PET-based model which may identify the patients at "high" risk of progressing after ASCT who are most likely to benefit from clinical trials examining different modalities of consolidative therapy (Figure 1D). Validation of this model is required in a larger independent population. Disclosures Ritchie: Amgen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy; BMS: Research Funding; Takeda: Research Funding; Beigene: Research Funding; Imago: Research Funding; Novartis: Honoraria; Sanofi: Honoraria. MacManus:National Health and Medical Research Council Australia: Research Funding. Seymour:Janssen: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria; Roche: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Gilead: Honoraria; Acerta: Consultancy, Honoraria. Dickinson:GlaxoSmithKline: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding, Speakers Bureau; Merck Sharpe and Dohme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Richter syndrome (RS) is the transformation of chronic lymphocytic leukemia (CLL) to a high-grade B-cell lymphoma and is associated with an aggressive clinical course and poor prognosis. Conventional treatment options for RS are generally associated with low response rates and limited durability making this entity an area of significant unmet therapeutic need. Immune checkpoint inhibitor therapy has shown promise in the treatment of some aggressive lymphoma subtypes. In RS, modest benefits have been reported in small phase two trials of anti-PD-1 monotherapy and in combination with ibrutinib, however larger scale studies are lacking (Ding et al Blood, 2017; Jain et al Blood, 2016). We sought to characterise the immune-evasion phenotype of RS focussing on potential genetic biomarkers which may inform the selection of patients who are most likely to benefit from immune-directed therapies. We first assessed the gene expression of immune-checkpoint molecules given their potential clinical relevance and ability to be targeted by available therapeutic agents. Given immunohistochemical (IHC) assessment of immune-checkpoint molecules is recognized to be associated with high inter-observer variability and there is a high correlation between gene expression of immune-checkpoint molecules and IHC, we performed gene expression quantification using the Nanostring nCounter Human Immunology V2 panel (Nanostring Technologies, USA). Nanostring analysis was performed on samples from 17 patients with histologically confirmed RS (DLBCL subtype) and compared to 73 cases of de novo (non-transformed) DLBCL. Significant differences in the gene expression of checkpoint molecules was observed between RS and DLBCL biopsies, including higher expression of LAG3, PD1 and TIGIT in RS (p=0.0001, logFC 1.9; p=0.0017, logFC 1.1 and p=0.0437, logFC 0.7 vs DLBCL, respectively). PD-L2 and TIM3 gene expression were both significantly lower in RS compared to DLBCL (p = 0.0059, logFC 0.8; p = 0.012, logFC 0.8). PDL1 and CTLA4 gene expression did not significantly differ between RS and DLBCL. We next assessed the gene expression of T- and NK- cell markers (including CD3, CD4, CD8, FOXP3 and CD56) and the ratios of these markers to malignant B-cells (CD19). We observed no significant difference between RS and DLBCL, consistent with a similar relative quantity of immune cell infiltration between the two entities. Significantly higher gene expression of CD39, a marker of CD8+ T-cell exhaustion, was observed in RS than DLBCL (p = 0.031; logFC 0.5). Additional immune-related genes were next assessed, including those involved in antigen presentation (e.g. B2M, HLA molecules, TAP), immunosuppressive cytokine generation (e.g. ARG1, IDO1) and apoptosis resistance (e.g. FAS) which showed no significant differences in expression between RS and DLBCL. To assess whether these findings were consistent across other transformed lymphoma subtypes, we compared RS to a cohort of transformed follicular lymphoma (tFL, n=16) and transformed marginal zone lymphoma (tMZL, n=25). LAG3 expression was significantly higher in RS compared to both tFL and tMZL (p=0.0002, logFC 2.7; p=0.019, logFC 1.7). PD1 expression was also significantly higher in RS than tFL but not tMZL (p=0.0045, logFC 1.7; p=0.39, logFC 0.4). Given the established association of copy number amplifications involving immune checkpoint molecules (e.g. PD-L1/PD-L2 on 9p24.1) representing a potential predictive biomarker of response in other lymphomas, we performed hybridization-based NGS with whole genome copy number assessment to evaluate immune checkpoint gene loci in the three cohorts. No significant focal amplifications were detected in RS samples with overexpressed immune-checkpoint molecules. In contrast, three patients in the DLBCL/transformed cohort had focal copy number amplifications involving PD-L1. No copy number amplification of LAG3 was observed in either RS or DLBCL. In summary, we have observed significantly increased gene expression of LAG3, PD1 and TIGIT in RS compared to de novo DLBCL. Combined with increased gene expression of the exhausted cytotoxic T-cell marker CD39, these data provide a strong biological rationale for pursuing LAG3 inhibition either alone or in combination with other immune checkpoint blockade to enhance anti-tumour T cell responses in this difficult-to-treat entity. CG/JL/YK co-first authors Disclosures Gould: NovoNordisk: Other: Travel funding - domestic flights to attend education, May 2018. Villa:Roche, Abbvie, Celgene, Seattle Genetics, Lundbeck, AstraZeneca, Nanostring, Janssen, Gilead: Consultancy, Honoraria. Tam:Abbvie, Janssen: Research Funding; Abbvie, Janssen, Beigene, Roche, Novartis: Honoraria. Neeson:Roche Genetech: Research Funding; Allergan: Research Funding; Juno/Celgene: Research Funding; Compugen: Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Seymour:Roche: Consultancy, Research Funding, Speakers Bureau; Takeda: Consultancy; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Acerta: Consultancy; Celgene: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding. Dickinson:Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Merck Sharpe and Dohme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; GlaxoSmithKline: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Blombery:Invivoscribe: Honoraria; Novartis: Consultancy; Janssen: Honoraria.