Background: NIVO + chemo demonstrated superior overall survival (OS) and clinically meaningful progression-free survival (PFS) benefit vs chemo and an acceptable safety profile in previously untreated, advanced non-HER2+ GC/GEJC/EAC, leading to approvals in many countries. NIVO + chemo continued to demonstrate clinically meaningful improvement in efficacy at 2 and 3-yr follow-ups. We present 4-yr follow-up results for NIVO + chemo vs chemo from CheckMate 649. Methods: Adults with previously untreated, unresectable advanced, or metastatic GC/GEJC/EAC were enrolled, regardless of programmed death ligand 1 (PD-L1) expression. HER2+ patients (pts) were excluded. Randomized pts received NIVO (360 mg Q3W or 240 mg Q2W) + chemo (XELOX Q3W or FOLFOX Q2W), NIVO + ipilimumab, or chemo. Dual primary endpoints for NIVO + chemo vs chemo were OS and PFS by blinded independent central review (BICR) in pts with PD-L1 combined positive score (CPS) ≥ 5. Results: 1581 pts were randomized to NIVO + chemo or chemo. At the 48-month (mo) minimum follow-up, NIVO + chemo continued to demonstrate OS and PFS benefit vs chemo in pts with PD-L1 CPS ≥ 5 and all randomized pts (Table) OS benefit with NIVO + chemo was observed in most prespecified subgroups. Objective response rates (ORR) were higher and responses were more durable with NIVO + chemo vs chemo in pts with PD-L1 CPS ≥ 5 and all randomized pts (Table). In the exploratory analysis of OS by response at the 18-week landmark timepoint, there were numerically more pts achieving response with NIVO + chemo vs chemo, and median OS (95% CI) with NIVO + chemo was numerically longer in responders vs non-responders both in pts with PD-L1 CPS ≥ 5 (20.5 [17.5–25.0] vs 14.0 [11.6–15.7]) and all randomized pts (19.4 [17.5–21.7] vs 13.1 [11.6–14.4]). No new safety signals were identified, consistent with the 3-yr follow-up. Conclusions: NIVO + chemo is the first PD-1 inhibitor/chemo combination to demonstrate long-term efficacy and acceptable safety after 4 yrs of follow up in previously untreated advanced GC/GEJC/EAC. These results are consistent with earlier follow-ups, further supporting NIVO + chemo as a standard 1L treatment in these pts. Clinical trial information: NCT02872116.

^aPer BICR.

^bIn pts with measurable target lesions at baseline.

^cIn responders.