Ultrastructural and immunohistochemical study of epithelioid hemangioendothelioma of bone: coexpression of epithelial and endothelial markers.

Four cases of epithelioid hemangioendothelioma of bone--a borderline malignant tumor of vascular origin--were studied ultrastructurally and immunohistochemically. The epithelioid tumor cells were positive for vimentin, polyclonal and monoclonal cytokeratins, and the endothelial markers factor VIII-related antigen (FVIII:RAg) and Ulex europaeus agglutinin I. The coexpression of polyclonal cytokeratin and FVIII:RAg was demonstrated by means of step sections in the same tumor cells. The endothelial origin of epithelioid tumor cells was supported ultrastructurally by identification of Weibel-Palade bodies.