Abstract Background Nivolumab was approved for the treatment of advanced gastric cancer in 2017 in Japan. The aim of this study was to assess the impact of nivolumab in a real‐world clinical setting. Methods This single‐institutional retrospective study included patients with advanced gastric or esophagogastric junction adenocarcinoma and a history of first‐line chemotherapy with platinum‐based doublet or triplet regimens between 2010 and 2020. To assess the impact of nivolumab on survival, the patients were divided based on the year of nivolumab approval into a pre‐2017 (2010–2016) group and a post‐2017 (2017–2020) group. Results From a total of 1918 patients, 1093 were excluded. There were 533 patients in the pre‐2017 group and 292 in the post‐2017 group. Immune checkpoint inhibitors were used significantly more often in the post‐2017 group than in the pre‐2017 group (8.6% vs. 47.9%). Median overall survival was significantly longer in the post‐2017 group (16.9 vs. 13.9 months; hazard ratio [HR] 0.75, 95% confidence interval [CI] 0.63–0.90; p &lt; 0.01). The proportion of patients transitioning to third‐line treatment was higher in the post‐2017 group than in the pre‐2017 group (56.3% vs. 43.8%, p &lt; 0.01). Median survival outcomes following progression on second‐line treatment were significantly longer in the post‐2017 group (4.3 vs. 3.2 months; HR 0.70, 95% CI 0.57–0.86; p &lt; 0.01). Conclusion The proportion of patients transitioning to third‐line treatment and survival outcomes following progression on second‐line treatment have improved since the approval of nivolumab. This drug might help to prolong overall survival in real‐world practice.

Impact of immune checkpoint inhibitors on survival outcomes in advanced gastric cancer in Japan: A real‐world analysis