Background: In CheckMate 577 (NCT02743494), NIVO demonstrated a significant and clinically meaningful improvement in disease-free survival (DFS; primary endpoint) vs placebo (PBO) and was well tolerated in patients (pts) with resected (R0) stage II/III EC/GEJC who received neoadjuvant CRT and had residual pathologic disease. Median DFS doubled with NIVO vs PBO (22.4 vs 11.0 months; HR 0.69; 96.4% CI 0.56–0.86; P = 0.0003). Serious treatment-related adverse events (TRAEs) and TRAEs leading to discontinuation were reported for < 10% of pts with NIVO and 3% with PBO. Methods: Pts were randomized 2:1 to NIVO 240 mg or PBO Q2W for 16 weeks, followed by NIVO 480 mg or PBO Q4W. Here, we present additional efficacy, safety, and quality-of-life (QoL) data from CheckMate 577. Results: 794 pts were randomized (NIVO, 532; PBO, 262). Distant recurrence was reported for 29% vs 39% and locoregional recurrence for 12% vs 17% of pts in the NIVO vs PBO groups, respectively. Median distant metastasis-free survival was 28.3 vs 17.6 months with NIVO vs PBO (HR 0.74; 95% CI 0.60–0.92). Median progression-free survival 2 (PFS2; time from randomization to progression after subsequent systemic therapy, initiation of second subsequent systemic therapy, or death, whichever is earlier) was not reached with NIVO vs 32.1 months with PBO (HR 0.77; 95% CI 0.60–0.99). TRAEs with potential immunologic etiology (select TRAEs; sTRAEs) reported for NIVO are presented in the table. Results for the FACT-ECS and FACT-G7 showed similar trends for QoL improvement from baseline for NIVO and PBO during treatment and maintained benefit post-treatment. Conclusions: Adjuvant NIVO demonstrated clinically meaningful efficacy, an acceptable safety profile, and maintained QoL, providing further support for its use as a new standard of care for pts with resected EC/GEJC who received neoadjuvant CRT with residual pathologic disease. Clinical trial information: NCT02743494

^aMost sTRAEs were grade 1 or 2. Grade 3–4 sTRAEs occurred in ≤ 1% of pts and there were no grade 5 sTRAEs. ^bEvents without a stop date or where stop date was death date were considered unresolved; events without worsening from baseline were excluded.