Background: G-len has promising activity and manageable toxicity in R/R FL (Morschhauser et al. 2019). We report the final analysis of an open-label, multicenter, Phase Ib/II trial (NCT02631577) that evaluated the immunomodulatory triplet G-atezo-len in pts with R/R FL. Methods: An initial 3+3 dose‐escalation to identify the Phase II len dose was followed by an expansion phase with G-atezo-len. Enrolled pts (aged ≥18 years) received induction with 6, 28-day cycles of G 1000 mg IV on Day [D] 1, 8, and 15 of Cycle [C] 1 and D1 of C2–6, atezo 840 mg IV on D1 and 15 of C2–6, and len 15/20 mg (dose escalation) or 20 mg (expansion) orally on D1–21 of C1–6. Responders received 24 months (mos) of maintenance with G 1000 mg D1 every 2 mos, atezo 840 mg D1–2 every mo, and len 10 mg D1–21 mos 1–12. The primary endpoint was complete response at end of induction by PET-CT assessed by Independent Review Committee (modified Lugano 2014 criteria; Morschhauser et al. ICML 2019). Exploratory endpoints described herein included progression-free survival (PFS), overall survival (OS), and duration of response (DOR). Adverse events (AEs) were also assessed. Results: At the final analysis (October 7, 2020), 38 pts had completed the trial. Median age was 62 years, 26% had a high-risk FLIPI score, 45% were refractory to their last line of therapy, and 37% had progression of disease within 24 mos of their first-line of therapy (POD24). Median treatment duration was 26 mos (range: 0.4‒30). The 36-mo PFS rate for the overall population (median observation time, 35.9 mos; range: 3‒47) was 64% (95% CI, 45‒79), OS was 85% (95% CI, 70‒93), and median DOR was 38 mos (95% CI, 35‒NE). 36-mo PFS rates for the following subgroups are provided in the table: double refractory (rituximab and an alkylator); with/without POD24; minimal residual disease (MRD) +/-. In total, 32 pts (84%) had a Grade 3/4 AE (majority hematologic), and 18 (47%) had a serious AE. Five pts (13%) during induction and six pts (16%) during maintenance had an AE that led to discontinuation of any drug. Two fatal AEs were reported (1 merkel carcinoma, 1 sarcomatoid carcinoma; both unrelated to any study drug). The most common atezo AEs of special interest were hyperthyroidism (13%), hypothyroidism (11%), increased ALT and AST (both 8%), increased lipase (8%), and hepatocellular injury (5%). Conclusions: G-atezo-len is efficacious in pts with R/R FL, with data from the final analysis suggesting a potential for improved outcomes versus the G-len doublet. AEs were consistent with the safety profile of the individual drugs. Clinical trial information: NCT02631577

*All pts progressed before 36 mos; median PFS was 10.7 mos (range: 1.8‒18).