Gastric carcinosarcoma (sarcomatoid carcinoma) with rhabdomyoblastic and osteoblastic differentiation.

A rare case of carcinosarcoma (sarcomatoid carcinoma) with rhabdomyoblastic and osteoblastic differentiation occurring in the gastric remnant is reported. A 69-year-old Japanese man who had undergone a partial gastrectomy for a duodenal ulcer 30 years earlier, presented with anemia, epigastralgia, and an abdominal mass. The diagnosis of gastric carcinosarcoma was made based on the findings of endoscopic biopsies. The patient was thus scheduled to undergo a surgical operation, but he died of respiratory failure. At autopsy, a huge polypoid tumor measuring 20 x 18 x 8 cm was located on the greater curvature of the gastric remnant. Microscopically, the tumor consisted of intimately mixed tubular adenocarcinoma and heterologous mesenchymal elements containing rhabdomyosarcoma and osteosarcoma. Between these components, a morphological transition from the adenocarcinoma element to the sarcomatous element was observed. Ultrastructually, rhabdomyoblastic differentiation was confirmed in the sarcomatous areas. Immunocytochemical expressions of epithelial markers including epithelial membrane antigen and cytokeratins (35bH11 and 34bE12) were recognized not only in the carcinomatous cells but also in the sarcomatous cells. These findings suggest that carcinomatous cells appear to transform into cells with sarcomatous features.