A case of advanced gastric cancer responding to S-1 therapy, leading to pathologically complete response

Our patient was a 74-year-old man with abdominal pain. A gastrofiberscope revealed type 2 advanced gastric cancer. An abdominal computed tomography(CT)demonstrated liver and lymph node metastases. The No. 8a lymph node was 7 cm in diameter, and it invaded the head of the pancreas. Since a curative operation was deemed impossible, S-1 was administered orally for 28 consecutive days with a 14-day interval. After 2 courses of monotherapy, CT showed that metastatic lymph nodes were reduced and that liver metastases had mostly disappeared. After 8 courses, the primary lesion was scarred and the lymph node metastases were remarkably reduced. Therefore, we conducted distal gastrectomy and lymph node resection (D2). Histological findings revealed that there were no cancer cells in either the primary tumor or the lymph nodes, meaning that the resected lesions were Grade 3 in pathology. This rare case showed that S-1 monotherapy enabled curative surgery of unresectable gastric cancer with pathological CR.