BACKGROUND: Mantle cell lymphoma is characterized by short remissions and a median overall survival (OS) of less than 6 years with standard chemotherapy. We previously reported results of a single-arm phase II clinical trial of intensive chemotherapy induction with R-MACLO-IVAM followed by thalidomide maintenance with promising progression-free survival (PFS) and OS (Lossos et al. Leuk Lymph 2010). A subsequent single-arm phase II clinical trial assessing rituximab (R) rather than thalidomide maintenance was conducted and preliminary data communicated (Hosein et al. Am J Hematol 2015). We now present the final results of these studies. METHODS: Two prospective single-arm phase II clinical trials conducted at the University of Miami were IRB approved. Eligible patients were chemotherapy-naïve with confirmed diagnosis of MCL using WHO criteria, age 18-75 years, ECOG PS: 0-2, adequate organ function and no history of HIV or prior cancer. Pretreatment staging included CT and PET scans, colonoscopy and bone marrow biopsy. The chemotherapy regimen has been previously described (Lossos et al. Leuk Lymph 2010). Patients who achieved complete responses (both radiologically and pathologically) were eligible for the maintenance phase. Between June 2004 and 2019, 44 patients were enrolled; the first 22 patients received maintenance therapy with thalidomide (200 mg daily until relapse/intolerable toxicity) and a subsequent cohort of 22 patients received R (375mg/m2 IV weekly x 4 weeks, repeated every 6 months for 3 years). OS was calculated from date of diagnosis to date of death or last follow up, and PFS from date of diagnosis to the date of pathological evidence of recurrence or death. Analysis was performed using the Kaplan-Meier method, and the log-rank or Wilcoxon test for group comparison. RESULTS: Median PFS in thalidomide and R cohorts were 7.8 and 8.1 years, and 10-year OS 63.6% and 57.8%, respectively. There was no statistically significant PFS or OS difference between patients treated with thalidomide or R maintenance (Wilcoxon p= 0.988 and p= 0.564, respectively). Therefore, all 44 patients were evaluable together for toxicity and 43 for response. Median age was 58 (range 39-73 years), most patients were males (35, 79.5%) and ECOG PS ≤ 1 (42, 95.5%). All patients had at least stage III disease, with bone marrow involvement in 38 (86.4%), gastrointestinal involvement in 23 out of 39 (59%), and elevated LDH in 14 (68.2%) patients. Ki67 was >30% in 20 (54.1%) and blastic variant in 6 (13.6%) patients. Most patients presented with IPI ≥ 3 (23, 52.3%) and intermediate-high MIPI (30, 68.1%) scores. 36 completed all 4 cycles of therapy, treatment was stopped in 6 after 3 cycles, and in 1 after 2 cycles. 1 patient died during the first cycle. Of the 43 patients completing 2 cycles of chemotherapy 41 (95.3%) achieved complete response (CR) and 2 (4.7%) partial response (PR). There were 23 (52.3%) events for PFS (19 relapses, 4 deaths without documented progression/relapse), and 14 (31.8%) total deaths over a median follow up of 6.7 years (range 1-15). The 5 and 10-year PFS were 54.9% (95%CI: 37.6-69.2%) and 39.2% (95%CI: 22.3-55.8%), respectively; median PFS 8 years (95%CI: 3.9-12.5 years). 5 and 10-year OS were 84.4% (95%CI: 68.4-92.7%) and 60.4% (95%CI: 41.2-75.1%), respectively; and median OS was not reached. PFS and OS were statistically significant shorter in the high-risk MIPI group than intermediate and low groups (5-year PFS rates: 23.1% vs. 53.8% vs. 92.9%, respectively, p<0.001; 5-year OS rates 59.8% vs. 100% vs. 92.3%, respectively, p<0.02). Patients with blastic variant (n=6) had a 5-year PFS and OS of 25% and 75%, respectively. There was a plateau in PFS and OS starting from 8 years in patients with low MIPI. Toxicities during chemotherapy were similar to what we previously reported (n=36). For 22 patients who received R maintenance, there were no unexpected toxicities. CONCLUSIONS: These phase II clinical trials implementing frontline R-MACLO-IVAM in MCL demonstrate high overall response rates (95.3% CR and 4.7% PR) with encouraging PFS and OS. Notably, high risk patients such as those with blastic variant and high-risk MIPI score also demonstrated favorable outcomes compared to historical controls. Results demonstrate that R-MACLO-IVAM is an effective regimen to induce long-term remission and survival in MCL, without need for consolidation with stem-cell transplant. Disclosures Alderuccio: OncLive: Consultancy; Puma Biotechnology: Other: Immediate family member; Agios: Other: Immediate family member; Foundation Medicine: Other: Immediate family member; Inovio Pharmaceuticals: Other: Immediate family member; Targeted Oncology: Honoraria. Alencar:Celgene: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees. Rosenblatt:Mologen AG: Employment; Kite Pharma: Employment; Synergys Technologies: Employment; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; Merck: Employment. Lossos:Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; Janssen Scientific: Membership on an entity's Board of Directors or advisory committees; NIH: Research Funding.