Vimentin-negative epithelioid sarcoma. The value of an immunohistochemical panel that includes CD34.

Virtually all reported cases of epithelioid sarcoma have been vimentin rich, and the coexpression of vimentin and keratin is considered a characteristic immunophenotype in these tumors. We report three cases of soft tissue tumors with histologic and clinical features consistent with epithelioid sarcoma, all of which failed to immunoreact by standard immunohistochemistry for vimentin using two different monoclonal antibodies. Antigen retrieval demonstrated focal vimentin staining in one case, whereas the other two remained negative. An extensive panel of immunohistochemical stains revealed strong diffuse staining with keratin and epithelial membrane antigen in all three cases as well as patchy membrane staining with an antibody to CD34. CD34 positivity is commonly seen in epithelioid sarcoma, but it is very rarely found in carcinomas. We conclude that these cases represent a unique immunophenotypic variant of epithelioid sarcoma that can be immunohistochemically confirmed, despite the lack of identifiable vimentin, by their immunoreactivity for keratin and CD34.