Ibrutinib Maintenance Following Induction For Untreated Mantle Cell Lymphoma (Mcl): Initial Safety Report.

7542 Background: Maintenance rituximab in MCL has improved survival, though the optimal approach is not yet defined. Ibrutinib, a selective BTK inhibitor, has profound activity in R/R MCL. Ibrutinib maintenance (I-M) following induction for treatment-naive MCL has not been explored. We report preliminary results of a multicenter phase II trial assessing efficacy and safety of I-M for MCL after frontline induction. Methods: Patients with MCL with CR/PR to frontline chemo-immunotherapy (+/- autoSCT) received I-M 560 mg daily for up to 4 years. Primary objective was 3 year PFS rate. Secondary objectives were PR to CR conversions, median OS at 4 years and toxicity with MRD assessments planned. Results: Accrual is complete with 36 patients, median age of 60 (range 46-90), 28 males, 28 with advanced stage and 9 with extranodal disease. 18 (50%), 7 (19%) and 11 (31%) had low vs intermediate vs high risk MIPI respectively. 8/24 patients had a Ki-67 > / = 30%. For induction, 17 (47%) received BR, 18 (50%) a cytarabine-based regimen, 1 (3%) R-CHOP. 18 (50%) had autoSCT in CR1 prior to enrollment. 33 (92%) and 3 (8%) had CR and PR with induction respectively with 1 PR to CR conversion on I-M. At median follow-up of 19 mos, 24/36 (67%) patients remain on I-M (median 15 cycles, range 1-49) with 1 PD and 1 death. TRAEs led to dose reductions/interruptions in 25 (69%) patients, including permanent dose reductions in 7 (19%) and treatment discontinuation in 9 (25%; Table). 3 additional patients discontinued I-M, 1 for endometrial adenocarcinoma, 1 PD, 1 death, cause unknown. Conclusions: Ibrutinib maintenance is feasible in MCL patients who respond to frontline chemo-immunotherapy +/- autoSCT with manageable toxicities consistent with prior reports of ibrutinib. Additional follow-up and MRD status correlations with PFS and OS will provide insight on clinical relevance for this approach. Clinical trial information: NCT02242097. [Table: see text]