Epithelioid sarcoma. An electron-microscopic and immunohistochemical study.

The present report is a light- and electron-microscopic and immunohistochemical study of 7 cases of epithelioid sarcoma. Formalin-fixed and paraffin-embedded material and in one case ethanol-fixed material from the tumors as well as control tissues were used for the immunohistochemical analysis. A positive reaction for cytokeratins was observed in all 7 tumors when using 3 different polyclonal antibodies and 1 of 3 monoclonal antibodies. All tumors were positively stained with monoclonal antibodies against the epithelial membrane antigen (EMA) and all except one with monoclonal antibodies against the human milk fat globule (HMFG 1 and 2). In all tumors there was a positive reaction for actin and vimentin, using monoclonal antibodies. Ultrastructurally the tumor cells were characterized by pinocytic vesicles, cytoplasmic projections surrounding lumen-like slits, desmosome-like cell junctions and abundant thin and intermediate filaments, sometimes forming condensed bundles and tonofilament-like structures. In one case there were numerous dense cytoplasmic bodies, up to 800 nm in diameter, apparently formed by condensed intermediated filaments. The tumor cells of epithelioid sarcoma share morphologic features and immunohistochemical properties with epithelial cells, which however does not exclude the possibility of a mesenchymal origin.