Epithelioid sarcoma: the spectrum of ultrastructural differentiation in seven immunohistochemically defined cases.

Seven epithelioid sarcomas were examined by light and electron microscopy and by immunohistochemical methods for the presence of vimentin and the epithelial markers keratin and epithelial membrane antigen. All the tumors displayed vimentin and both epithelial markers. Electron microscopy showed a spectrum of cellular differentiation from primitive fibrohistiocytic cells to epithelial-type cells with junctions, microvilli, and tonofilaments. Spindle cells showed myofibroblastic and fibroblastic differentiation. Epithelioid sarcoma appears to be a tumor of primitive cells with the potential for mesenchymal and epithelial differentiation, like some embryonic tumors.