8004 Background: The GELA sponsored intergroup PRIMA Phase III study investigated 2 years of rituximab (R) maintenance in follicular lymphoma (FL) patients responding to first-line immunochemotherapy consisting of either 8 cycles of R-CVP, or 6 cycles of R-CHOP or R-FCM (plus 2 additional rituximab infusions). Methods: 1,217 patients were enrolled from 223 centres (25 countries) between Dec 2004 and Apr 2007. Pre-induction characteristics: median age 56 years (range 22–87); 52% male; 90% Ann Arbor stage III-IV; 33% B symptoms; 56% bone marrow involvement; 4% ECOG performance status >1; 34% elevated LDH; 32% β2-microglobulin >3mg/L; 21% FLIPI 0-1: 36% FLIPI 2; 43% FLIPI 3-5. Most patients (75%) received R-CHOP induction (22% R-CVP, 3% R-FCM). 1,018 eligible patients responding to induction therapy were randomized (stratified by regimen and response to induction) to observation or R-maintenance, 375 mg/m2 i.v. every 8 weeks for 2 years. Results: The primary endpoint of PFS was met at the planned interim analysis (ITT: 513 observation, 505 rituximab maintenance). Median follow-up was 25 months from randomization (31 months from study entry). There was a significant (stratified log-rank, P<.0001) improvement in the primary endpoint PFS, for R-maintenance (hazard ratio [HR]=0.50; 95% CI [0.39-0.64]; 2-year PFS 82%; 95% CI [78-86%] vs 66% [61-70%] for observation). An independent response review committee confirmed the significant improvement in PFS in the R-maintenance arm (HR=0.53 [0.41-0.68]). Time to next anti-lymphoma treatment, as well as response rate at the end of maintenance or observation, were significantly improved in the R-maintenance arm. The most common AEs were infections (22% observation, 37% R-maintenance). Grade 3-4 AEs were reported in 16% (observation) and 22% (R-maintenance) of patients (neutropenia 1% vs 4%; infections 1% vs 4%, respectively). Conclusions: The PRIMA study demonstrates that 2 years of R-maintenance therapy after induction immunochemotherapy in previously untreated FL significantly improves PFS with little additional toxicity. The PRIMA study provides evidence for a new standard of care for FL patients in need of treatment. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Roche Roche Genentech, Roche Roche