Epithelioid sarcoma. An immunohistochemical study.

The immunohistochemical findings in 14 epithelioid sarcomas, neoplasms of uncertain histogenesis, indicate that they react with antibodies against cytokeratin, epithelial membrane antigen, and vimentin. All cases were nonreactive for leukocyte common antigen, myoglobin, and Factor VIII-related antigen. These results point to the fact that epithelioid sarcoma expresses phenotypic characteristics more often associated with epithelioid neoplasms, rather than the mesenchymal profile of most soft tissue sarcomas. One explanation for this observation is that epithelioid sarcoma is in fact a carcinoma originating in the deep soft tissues. On the other hand, the pluripotential mesoderm has a known embryonic capacity to differentiate into epithelium and, therefore, it is plausible that epithelioid sarcoma is a mesenchymally derived neoplasm. Aside from histogenetic considerations, epithelioid sarcoma may be confused with a number of other neoplastic and granulomatous processes. Differential immunohistochemical stains are useful in selected instances wherein light and electron microscopic findings are diagnostically equivocal.