Epithelioid sarcoma was first described by Enzinger in 1970 as a rare soft tissue sarcoma that mimics granulomatous disease, carcinoma, and synovial sarcoma. The tumor typically presents as a painless, slow-growing soft tissue swelling in the distal extremity of young adult males. It is locally invasive and frequently metastasizes to regional lymph nodes and distant sites, most commonly to the lungs. Complete surgical resection is curative in low-stage disease; however, a risk of recurrence and late metastasis remains. Epithelioid sarcomas are tumors of purportedly mesenchymal origin that show ultrastructural and immunophenotypic evidence of epithelial differentiation. The mixed differentiation of epithelioid sarcoma can make the differential diagnosis challenging from a histopathologic perspective. The differential diagnosis is narrowed by the somewhat unique epithelioid sarcoma immunophenotype expressing cytokeratin, epithelial membrane antigen, and CD34. Epithelioid sarcoma is one of only a few tumors that characteristically lacks INI-1/SMARCB1 expression.
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