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Gastric carcinosarcoma with neuroendocrine differentiation as the carcinoma component and leiomyosarcomatous and myofibroblastic differentiation as the sarcomatous component

Gastric carcinosarcoma with neuroendocrine differentiation is a very rare neoplasm. In this article we present such a case. The gastroendoscopic examination of a 59‐year‐old Japanese man disclosed gastric cancer during follow‐up after operation for rectal cancer. Subsequently, total gastrectomy was carried out because of gastric cancer. A large tumor measuring 9.2×8.4 cm was observed in the posterior wall of the upper portion of the stomach. The tumor was composed of carcinoma and sarcomatous cells, and the histological transition of both components was observed. Immunohistochemically, carcinoma and sarcomatous cells were positive for cytokeratin CAM5.2. The carcinoma contained adenocarcinoma and malignant cells with neuroendocrine differentiation. The sarcomatous component showed leiomyosarcomatous and myofibroblastic differentiation. The present tumor is the fifth case of gastric carcinosarcoma with neuroendocrine differentiation and the first case of gastric carcinosarcoma with myofibroblastic differentiation. Pathologists should bear in mind that gastric carcinosarcoma may show various types of differentiation.