Conversion surgery for stage IV gastric cancer with a complete pathological response to nivolumab: a case report.

Background: Patients with stage IV gastric cancer have a poor prognosis despite the recent development of multidisciplinary treatments that include chemotherapy. However, conversion surgery has emerged as a promising strategy to improve the prognosis in responders with unresectable gastric cancer after chemotherapy. Moreover, nivolumab is currently recommended as a third-line treatment in patients with unresectable advanced gastric cancer. However, there are few reports of conversion surgery after nivolumab in patients with stage IV gastric cancer.

Case Presentation: A 68-year-old woman complaining of nausea was diagnosed with stage I gastric cancer (T2N0M0). Although we planned gastrectomy with lymphadenectomy, multiple liver metastases were detected during the surgery. After staging laparoscopy, we diagnosed this patient as having stage IV unresectable gastric cancer, and we administered chemotherapy and immunotherapy for 39 months (first-line regimen: 6 courses of S-1 plus oxaliplatin; second-line regimen: 6 courses of ramucirumab plus paclitaxel; and third-line regimen: 20 courses of nivolumab). Although the liver metastases completely disappeared after the second-line chemotherapy, lung metastases and a rapid enlargement of the primary tumor were confirmed. Consequently, the patient received nivolumab at a dose of 3 mg/kg intravenously every 2 weeks, then a dose of 240 mg/kg intravenously every 2 weeks from September 2018. After 20 courses of nivolumab, the primary tumor dramatically shrank and the lung metastases disappeared. The patient had a partial primary tumor response to nivolumab. Therefore, the patient underwent laparoscopic distal gastrectomy with D2 lymph node dissection. The macroscopic examination of the resected specimen showed an ulcer scar in the primary tumor site. The pathological examination demonstrated no residual tumors and no lymph node metastases, and the histological response of the primary tumor was categorized as grade 3. The postoperative course was uneventful, and the patient is receiving nivolumab to control potential liver and lung metastases.

Conclusions: Conversion surgery might help control tumor progression in responders after chemotherapy and immunotherapy.