Aberrant EMA expression in dermal cellular fibrous histiocytoma with central necrosis and epidermal ulceration: a potential mimicker of epithelioid sarcoma

We report a case of cellular fibrous histiocytoma (CFH) occurring as a polypoid, dermal nodule in the arm of a 10-year-old boy. Tumor, predominantly composed of spindle-shaped cells with mild degree of nuclear pleomorphism, showed as unusual morphological features central necrosis and epidermal ulceration. Apart from vimentin and CD10, surprisingly neoplastic cells were diffusely stained with EMA (epithelial membrane antigen). Although EMA expression is absent in conventional fibrous histiocytoma, immunoreactivity for this marker has been reported in about 60% of dermal epithelioid cell fibrous histiocytoma. This is the first case of CFH which exhibits diffuse EMA expression. The presence of tumor necrosis and epidermal ulceration, along with aberrant EMA expression, raised serious diagnostic problems with epithelioid sarcoma. Immunohistochemical analyses, showing diffuse nuclear INI1 (hSNF5/SMARCB1) expression and the absence of pancytokeratins, were extremely helpful in ruling out epithelioid sarcoma. Awareness that dermal CFH may concurrently exhibit necrosis, epidermal ulceration and diffuse EMA expression is crucial to avoid a misdiagnosis of malignancy.