Background: NIVO is the first adjuvant therapy to provide a statistically significant and clinically meaningful improvement in disease-free survival (DFS) versus PBO in resected EC/GEJC following neoadjuvant chemoradiotherapy as demonstrated by CheckMate 577. NIVO was well tolerated with an acceptable safety profile. This analysis provides additional information on the exploratory HRQoL endpoints in this clinical trial. Methods: The effect of NIVO versus PBO on HRQoL, including general and disease-related symptoms, functioning, disease burden, and overall QoL, was assessed using FACT-E and EQ-5D-3L patient-reported outcome (PRO) questionnaires administered at baseline (BL), every 4 weeks during the 12-month treatment period, and at post-treatment follow-up visits (up to 2 years after last dose). Longitudinal change from BL in PRO scores over 12 months was assessed using descriptive statistics. Additionally, mixed model for repeated measures and time to deterioration analyses evaluated the difference between treatment with NIVO and PBO (data not shown). Results: 794 pts with EC/GEJC were randomized 2:1 to NIVO (n = 532) or PBO (n = 262). PRO completion rates were ≥ 95% at BL and ~ 90% at 12 months on treatment. Mean (SD) BL HRQoL scores were similar between treatment arms for the FACT-E total score (NIVO: 133.40 [20.97]; PBO: 134.03 [20.40]); esophageal cancer subscale (ECS; NIVO: 50.2 [9.3]; PBO: 50.1 [8.9]); EQ-5D Visual Analogue Scale (NIVO: 70.4 [22.3]; PBO: 69.1 [24.1]); and EQ-5D Utility Index (NIVO: 0.820 [0.179]; PBO: 0.831 [0.163]) based on the UK value set. Descriptive analyses showed a trend for increases from baseline at most time points through week 49 for both NIVO and PBO treatment groups for FACT-E total score, ECS, and EQ-5D Visual Analogue Scale and Utility Index. Conclusions: Preliminary results from CheckMate 577 demonstrated that pts on NIVO treatment showed trends of improvement in both esophageal-specific and general HRQoL. Similar trends were also observed in pts treated with PBO over 1 year. Pts treated with NIVO did not experience a reduction in HRQoL, further supporting clinical data to demonstrate treatment benefit and tolerability for adjuvant NIVO in pts with resected EC/GEJC. Clinical trial information: NCT02743494