[A patient with small intestinal cancer and extensive lymph node metastasis who responded to S-1].

: The patient was an 89-year-old male who consulted our hospital with a complaint of black stools. He had undergone gastrectomy and Roux-en Y reconstruction. Upper digestive tract endoscopy revealed a flat plate-like ulcer in the jejunum on the anal side of the gastrojejunostomy site. Biopsy findings suggested undifferentiated adenocarcinoma. Computed tomography (CT) showed cervical, mediastinal, and intraperitoneal lymph node swelling, suggesting metastasis. Extensive lymph node metastasis made curative resection impossible, and symptoms such as perforation/stenosis were absent. Therefore, surgery was not performed, and systemic hemotherapy with S-1 (80 mg/body/day) was administered. We repeated 2-week administration and 1-week discontinuation per course. After the end of the second course, upper digestive tract endoscopy revealed cicatrization of the ulcer, and CT showed a marked decrease in the lymph node size; a complete response (CR) was achieved. During the 7-month follow-up after the initial consultation (7 courses of S-1 therapy in all), there has been no exacerbation, and the quality of life (QOL) has been maintained.