Abstract

Epithelioid fibrous histiocytoma (EFH) is a rare benign cutaneous mesenchymal neoplasm that harbors ALK gene rearrangement. A 20-year-old African American female presented with a right dorsal foot mass. It had been present since childhood (approximately 10 years) at first resembling a “mole” but changing and bleeding over the past year. The histopathological evaluation of the excisional biopsy showed bland spindle cells arranged in a storiform growth pattern with CD34 expression and scattered benign pigmented dendritic melanocytes, features concerning for the pigmented variant of dermatofibrosarcoma protuberans (DFSP, Bednar tumor type). However, there were also zones with plump histiocytoid cells in the superficial dermis resembling epithelioid fibrous histiocytoma. SOX-10 and HMB-45 highlighted the pigmented spindle cells, supporting melanocytic differentiation; the non-pigmented lesional cells were negative for SOX-10 and HMB-45. Breakapart fluorescence in situ hybridization (FISH) analysis for PDGFB and PDGFD rearrangement were negative, essentially excluding DFSP. The spindled and histiocytoid cell populations were both ALK-1 immunoreactive. FISH revealed an ALK rearrangement, supporting a diagnosis of epithelioid fibrous histiocytoma. Given the unusual features, the mass was completely excised with negative margins. At 27 months follow-up, the patient reports no recurrence of the lesion. We believe this represents an unusual, spindled variant of epithelioid fibrous histiocytoma with pigmented dendritic melanocytes that has not been previously reported to our knowledge. This variant is important because it could easily be confused with pigmented DFSP, a malignant tumor that would be treated more aggressively.