[A Case of Initially Unresectable Advanced Gastric Cancer Radically Resected by Conversion Surgery after Nivolumab Immunotherapy].

A 77-year-old man was admitted to our hospital with symptoms of epigastralgia and vomiting. Detailed investigation revealed unresectable advanced gastric cancer accompanied by multiple lymph node metastases and invasion of the pancreas(UM, type 3, cT4b, N3, M0, Stage ⅢC). The patient received nivolumab immunotherapy after first-line S-1 plus oxaliplatin(SOX)chemotherapy and second-line nab-paclitaxel(PTX)plus ramucirumab(RAM)chemotherapy. Remarkable tumor reduction was observed after 3 courses of nivolumab immunotherapy, and the patient subsequently underwent radical total gastrectomy with splenectomy and D2 lymphadenectomy. Histopathological examination of the resected stomach showed a near complete response, and only small metastatic foci remained in No. 2 lymph nodes, resulting in R0 resection. The patient was followed up without adjuvant therapy, and he is alive 6 months after the treatment without any symptoms of recurrence. The mechanism of action of immune checkpoint inhibitors is fundamentally different from that of conventional cytotoxic chemotherapeutic agents. Recently, several reports have described good responses to immune checkpoint inhibitors in cases where conventional chemotherapy has been unsuccessful. When predictive biomarkers of response to immune checkpoint inhibitors are identified, a combination therapy of preceding immunotherapy and subsequent surgery might provide an efficient radical therapeutic effect even in cases of unresectable advanced gastric cancer.