Carcinosarcoma of the stomach. A case report with light microscopic, immunohistochemical, and electron microscopic study.

A carcinosarcoma of the stomach in a 66-year-old man is reported. The tumor which had a diameter of 4 cm was an ulcerofungating mass in the posterior wall of the antrum. Histologically it was composed of well-differentiated adenocarcinoma admixed with sarcomatous elements which showed chondrocytic differentiation on light and electron microscopy. The sarcomatous areas were multifocally scattered in the central portion of the tumor and intimately blended with adenocarcinoma cells. CEA immunoreactivity was found not only in the adenocarcinoma but also in the transitional sarcomatous cells, supporting the hypothesis that this tumor might derive from mesenchymal metaplasia of a primarily epithelial neoplasm.