Pleomorphic angiomatoid fibrous histiocytoma: a case confirmed by fluorescence in situ hybridization analysis for EWSR1 rearrangement.

Angiomatoid fibrous histiocytoma (AFH) is a neoplasm of uncertain histogenesis with intermediate malignant potential. It occurs in superficial soft tissues in any age group and at any body site, although the typical example occurs on extremities in children/young adults. The neoplasm is usually composed of a bland histiocytoid proliferation of cells with eosinophilic cytoplasm forming a syncytium, often surrounded by a dense fibrous pseudocapsule and lymphoid infiltrate, with abundant intralesional hemorrhage forming blood-filled spaces. AFH may show striking pleomorphism and mitotic activity, and such cases can lead to confusion with other atypical mesenchymal lesions, including pleomorphic sarcomas. Recent findings have shown that a majority of cases of AFH have translocations involving the EWSR1 or FUS genes. We present a diagnostically challenging case of AFH with pleomorphic features and minimal lymphoid and angiomatoid changes involving the superficial subcutis and deep dermis on the scalp of an 8-year-old boy. "Areas with typical AFH morphology were identified and the diagnosis confirmed with identification of an EWSR1..." rearrangement detected by fluorescence in situ hybridization. Pleomorphic AFH should be included in the differential diagnosis of atypical mesenchymal tumors of skin and superficial subcutis and molecular testing may prove helpful in this regard.