[A Case of Unresectable Advanced Gastric Cancer with Pathological Complete Response to SOX plus Nivolumab Therapy].

The patient was a 79-year-old male diagnosed with gastric cancer with lung metastasis(cT3N2M1[PUL], cStage ⅣB)and sigmoid colon cancer(cT3N0M0, cStage Ⅱa). He underwent systemic chemotherapy with the SOX plus nivolumab regimen for unresectable advanced gastric cancer. Six months after the initiation of chemotherapy(9 courses), the primary tumor and lymph node metastases in the lesser curvature and suprapancreatic margin had shrunk, and the lung metastases had disappeared. However, chemotherapy was discontinued because of the development of immune-related interstitial pneumonia, and steroid therapy was initiated. Nine months after the initiation of chemotherapy, the tumor shrinkage rate remained constant and interstitial pneumonia improved; however, the patient was referred to our hospital for surgical treatment for gastric stenosis. A laparoscopic distal gastrectomy was performed for gastric cancer. Histopathological findings revealed no residual cancer cells in the primary tumor or lymph nodes, and the histological response was Grade 3. The patient remained recurrence-free for 10 months after the surgery. SOX plus nivolumab therapy for unresectable advanced gastric cancer is expected to have a high tumor-shrinkage effect, and combining it with conversion surgery may lead to an improved long-term prognosis.