Biliary carcinosarcoma arising in nonparasitic simple cyst of the liver.

We report a carcinosarcoma arising in a nonparasitic simple cyst of the liver. Sequential imaging findings revealed that the tumour originated in a hepatic cyst and was composed of well-differentiated tubular adenocarcinoma and high-grade spindle cell sarcoma without apparent transition between the two. At the margin of the tumour, a single layer of benign cuboidal epithelium and outer fibrous bands were present, suggesting that the tumour had arisen from a nonparasitic simple cyst of the liver. Immunohistochemically, carcinoma cells were positive for cytokeratins, epithelial membrane antigen and CA 19-9 and negative for vimentin, while sarcomatous cells were positive for vimentin and negative for cytokeratins, epithelial membrane antigen and CA 19-9. Sarcomatous cells did not show any immunophenotypic features of smooth muscle cells, striated muscle cells, histiocytes, lipocytes, nerve cells, Schwann cells or endothelial cells. Ultrastructurally, no specific differentiation was seen in the sarcomatous cells.