Background: Patients with MYC rearrangement positive large B cell lymphoma other than Burkitt lymphoma (MYC+ LBCL), have a dismal prognosis following standard first line therapy with R-CHOP. Retrospective studies report complete remission rates < 50% and 2-year overall survival (OS) of approximately 35%. Lenalidomide is an immunomodulatory drug and is able to down-regulate MYC and its target genes and proteins in B cells that harbor a MYC rearrangement. We report data of a prospective phase II study evaluating the efficacy of lenalidomide in combination with R-CHOP (R2CHOP) in newly diagnosed MYC+ LBCL patients.Methods: A national screening program for MYC rearrangement by fluorescence in situ hybridization (FISH) was performed in newly diagnosed LBCL patients. Patients with a proven MYC rearrangement, ≥ 18 year, Ann Arbor stage II-IV, were offered participation in a single arm phase II study. Treatment consisted of 6 cycles R-CHOP21 plus lenalidomide 15 mg on day 1-14, followed by two additional rituximab administrations. Use of G-CSF was mandatory. All patients received intrathecal methotrexate prophylaxis. 18F-FDG PET-CT (PET-CT) scans were performed at baseline, midterm (after 3 cycles) and end-of-treatment (EOT).Diagnostic lymphoma samples were centrally reviewed including immunohistochemical (IHC) work-up and complementary BCL2 and BCL6 FISH analysis. Cell of origin classification was determined by IHC (Hans) and by gene expression profiling (Lymph2Cx).The primary endpoint was complete metabolic response rate (CMR) on EOT PET-CT scan, according to the Deauville criteria and assessed by 2 independent nuclear medicine physicians performing central review. In case of discordance, a third adjudicator reviewed. Confirmation of bone marrow (BM) negativity at EOT for patients with positive BM at diagnosis was not required for CMR.Secondary endpoints included disease free survival (DFS), progression free survival (PFS), OS and predictive value of midterm PET-CT for EOT PET-CT scan. Data cut-off was July 4th 2018.Results: From April 2015 to February 2018, 85 patients were included at 20 hospitals. Planned interim analysis (after 26 consecutive patients completed treatment) revealed no safety concerns. At data cut-off, central data management, pathology and imaging review processes were completed for the first 60 patients. The remaining patients (60 to 85) are still on treatment or have recently finished treatment. Among the first 60 patients, 2 were declared ineligible, leaving 58 patients for this analysis (demographics and disease characteristics in table 1).Central pathology review confirmed diagnosis of MYC+ LBCL in all patients. Additional FISH analysis revealed that 41/58 patients (71%) had MYC and BCL2 and/or BCL6 rearrangements (double hit or triple hit), 11/58 (19%) had a single MYC rearrangement, 6/58 (10%) had a MYC rearrangement but no information on BCL2 and BCL6.At EOT PET-CT scan (primary endpoint), 36/58 patients (62%) were in CMR (95% confidence interval (CI) 50%-71%). 2/58 patients (3%) reached a partial metabolic response (PMR), and 20/58 patients (34%) had progressive disease (PD).At midterm PET-CT, 39/58 patients (67%) were in CMR; of these 29 were still in CMR and 10 showed PD at EOT PET-CT. 18/58 patients (31%) were in PMR at midterm; 7 of them converted to CMR, 2 remained in PMR, 9 showed PD at EOT. One patient went off protocol after two cycles due to progression.With a median follow-up of 17.2 months, 1-year estimates for OS were 79% (CI 66%-88%), for DFS 74% (CI 59%-85%), and for PFS 60% (CI 47%-72%).Grade 3 and 4 adverse events (AE) were seen in 26 (43%) respectively 9 patients (15%). Most common grade 3-4 AEs were gastrointestinal disorders, infections, and neutropenia. 55 serious AEs were reported in 27 patients (all hospitalization). 1 patient went off protocol due to grade 3 diarrhea.Univariate regression analyses revealed no significant prognostic factors for achieving CMR or prolonged survival yet.Conclusion: These data represent the first prospective trial worldwide for newly diagnosed MYC rearrangement positive LBCL patients. Treatment with R2CHOP demonstrates acceptable toxicity and promising efficacy with 62% CMR on centrally reviewed PET-CT scan and a 1-year OS rate of 79%. In December 2018, all 85 registered patients will have finished treatment and complete analysis of the primary endpoint and additional biological studies will be available.Disclosures Chamuleau: Gilead: Research Funding; celgene: Research Funding; Genmab: Research Funding; BMS: Research Funding. Mous: Gilead: Honoraria, 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 CILAG: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; MSD: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; sandoz: Membership on an entity's Board of Directors or advisory committees. Lugtenburg: takeda: Consultancy, Research Funding; servier: Consultancy, Research Funding; roche: Consultancy; BMS: Consultancy; Celgene: Consultancy; Sandoz: Consultancy; GenMab: Research Funding. Kersten: 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.↵* Asterisk with author names denotes non-ASH members.