Carcinosarcoma is a malignant tumor composed of both epithelial and mesenchymal malignant tumor components. A 78-year-old man was transferred to our hospital because of hematemesis and tarry stool. An emergency gastrointestinal endoscopic examination revealed active bleeding from an ulcerative lesion on the posterior wall of the gastric body
endoscopic hemostasis was successfully performed. A gastrointestinal endoscopy performed two months later showed a polypoid lesion at the same place where the ulcer had been. The biopsy specimen was histologically diagnosed as well to moderately differentiated tubular adenocarcinoma. The patient underwent a laparoscopic distal gastrectomy with D2 lymph node dissection under a diagnosis of gastric adenocarcinoma. A 28 × 15 mm polypoid tumor was resected from the gastric body, and was found on microscopic examination to consist of both carcinoma and sarcoma components, showing atypical spindle cells, which were positive for α-smooth muscular actin, calponin, and h-caldesmon, but negative for CD34, CD117 (c-kit), desmin, and dog 1. These findings led to a diagnosis of gastric carcinosarcoma. The tumor was confined to the mucous membrane. Lymph node metastasis was found in one node and contained only the carcinoma component. The postoperative course was uneventful. The patient lived without recurrence for 2 years. Carcinosarcoma of the stomach is a rare tumor with high malignant potential and poor prognosis. Careful follow up is required for early detection of any recurrence.