Malignant rhabdoid tumor of the liver. Evidence for epithelial differentiation.

Malignant rhabdoid tumors most commonly occur in the kidney. Rarely does this tumor arise in extrarenal sites; a single documented primary hepatic tumor has been described. We describe two patients who had malignant tumors arising in the liver. These tumors demonstrated cytologic, histologic, and ultrastructural features typical of malignant rhabdoid tumor. By immunohistochemistry, the tumor cells from both patients expressed the epithelial membrane antigen, cytokeratin, and vimentin and cells from one patient contained alpha 1-antitrypsin. Neither patient had evidence of renal involvement at autopsy. Thus, we demonstrate that this rapidly fatal tumor contains cells showing features of epithelial differentiation, and that it may occur as a primary hepatic tumor.