Stage IV gastric cancer with microsatellite instability-high achieving long-term survival by gastrectomy after nivolumab as third-line therapy: a case report and literature review.

We report a patient with highly advanced gastric cancer with peritoneal dissemination, which worsened during second-line therapy and was successfully treated with gastrectomy after nivolumab administration as a third-line therapy. MSI-high gastric cancer is a target that should be actively considered for the administration of ICIs, such as nivolumab, and multidisciplinary treatment combined with chemotherapy and gastrectomy, including conversion surgery, can lead to patients' long-term survival.