[A Case of Peritoneal Metastasis from an Unresectable Advanced Gastric Cancer with a Good Response to Nivolumab].

A 74-year-old woman presented with abdominal discomfort and was diagnosed with an unresectable advanced gastric cancer(T4aN3aM1, stage Ⅳ)based on a thorough examination. S-1/cisplatin therapy was administered as first-line treatment and paclitaxel/ramucirumab therapy as the second-line treatment. However, because the patient developed a peritoneal dissemination and her lymph node metastasis increased despite these regimens, nivolumab was introduced as a third- line treatment. The CT scan revealed that after the 5 courses of nivolumab, both the peritoneal dissemination and metastatic lymph nodes shrunk; after 12 courses of nivolumab, the peritoneal dissemination almost disappeared. Although nivolumab, an anti-programmed cell death-1(PD-1)antibody, has the possibility to cause immune-related adverse events not seen with conventional chemotherapy, in the present case, these events did not occur and the antitumor effects were maintained for a relatively long period without a decrease in the performance status(PS). We experienced a case of peritoneal metastasis from gastric cancer with a good response to nivolumab. Herein, this case is reported with some literature review.