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

The prognosis for stage IV gastric cancer remains poor; however, the advent of immune checkpoint inhibitors (ICIs) such as nivolumab has increased the number of patients with long-term survival. Patients with microsatellite instability (MSI)–high gastric cancer have been recognized as a highly effective population for ICIs. Herein, we report a patient with MSI–high advanced gastric cancer treated with gastrectomy after the administration of nivolumab as third-line therapy. A 73-year-old woman presented with a type 3 tumor in the lower part of the gastric body, which was diagnosed as gastric cancer through biopsy. Staging laparoscopy revealed that the tumor had invaded the pancreas and the posterior lobe of the transverse mesocolon, and disseminated nodules were found near the ligament of Treitz. After 4 courses of S-1 plus cisplatin therapy, laparoscopic gastrojejunal bypass was performed because of difficulty in oral intake. She received S-1 plus oxaliplatin therapy after a gastrojejunal bypass; however, her regional lymph nodes were enlarged. After six courses of paclitaxel plus ramucirumab as second-line chemotherapy, computed tomography (CT) showed exacerbation of peritoneal dissemination; thus, nivolumab was selected as the third-line therapy. The tumor was characterized by MSI–high. At 24 courses, CT and gastroscopy revealed a complete clinical response of the tumor; however, re-growth of the primary tumor was observed at 36 courses. The patient underwent distal gastrectomy with D1 + lymph node dissection, and received S-1 monotherapy as adjuvant therapy for 1 year. No recurrence was noted at 39 months after the surgery. 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.