The FDA approved nivolumab on May 20, 2021, for the adjuvant treatment of completely resected (negative margins) esophageal or gastroesophageal junction cancer (EC/GEJC) in patients who had residual pathologic disease following chemoradiotherapy. The approval was based on data from the double-blind CheckMate 577 trial, which randomly allocated patients to receive nivolumab or placebo. Disease-free survival (DFS) was the primary endpoint. At the time of the final DFS analysis and the prespecified interim overall survival (OS) analysis, the estimated median DFS was 22.4 months [95% confidence interval (CI), 16.6–34.0] in the nivolumab arm versus 11.0 months (95% CI, 8.3–14.3) in the placebo arm, with an HR of 0.69 (95% CI, 0.56–0.85; two-sided P value = 0.0003). An unblinded review of OS did not indicate a detrimental effect on survival. Adverse reactions occurring in ≥20% of patients receiving nivolumab were fatigue/asthenia, diarrhea, nausea, rash, musculoskeletal pain, and cough. Approval of nivolumab is likely to change the treatment paradigm for the adjuvant treatment of patients with completely resected (negative margins) EC/GEJC who have residual pathologic disease following chemoradiotherapy based on the study results and favorable risk:benefit of nivolumab administration.