Conversion surgery of Stage IV gastric cancer with peritoneal dissemination after nivolumab.

A 69-year-old man was clinically diagnosed as stage IV gastric cancer with peritoneal dissemination. We performed systemic chemotherapy consisting of S-1 plus oxaliplatin as a first line, and ramucirumab plus nab-paclitaxel as a second line. However, CT and EGD revealed growth of the primary tumor and the lymph nodes along the lesser curvature and adjacent to the cardia. In addition, CT revealed ascites in the rectovesical pouch. Therefore, treatment was switched to nivolumab. After 3 treatment courses, CT revealed shrinkage of lymph nodes and disappearance of ascites. After 12 courses of nivolumab, however, EGD revealed growth of the tumors in the stomach with minor hemorrhage, prompting the consideration of gastrectomy. At the time of laparotomy, the peritoneal dissemination had completely disappeared, and peritoneal cytology was negative. Therefore, total gastrectomy with D2 and paraaortic lymphadenectomy was performed, after 21 months following the initial diagnosis. To our knowledge, there are no previous reports that have demonstrated the disappearance of peritoneal dissemination and ascites in response to nivolumab, resulting in curative gastrectomy. © The Japan Society of Clinical Oncology 2021.