Abstract

We would like to share an interesting case of cutaneous PEComa, which was initially diagnosed as a lipidized variant of dermatofibroma due to immunoreactivity for Factor XIIIa. At the age of 15, our patient presented with a lesion on her left lateral malleolus. A biopsy was performed and interpreted at an outside institution as a lipidized variant of dermatofibroma. Four years later she presented to our Dermatology clinic with a 6.0 x 3.0 cm firm and fusiform mass at the original biopsy location. Dermatofibrosarcoma protuberans was considered clinically and a punch biopsy was performed. Histologic sections demonstrated a neoplasm composed of cells with abundant variably clear to slightly eosinophilic granular cytoplasm disposed as cords and sheets. The tumor cells exhibited positive immunoreactivity for pan-melanoma cocktail and HMB45, and focal immunoreactivity for Factor XIIIa. Additionally they were negative for SMA, desmin, S-100, SOX-10, NSE, cytokeratin stains, and hematopoietic markers. Perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal neoplasm of perivascular epithelioid cells with myomelanocytic differentiation. Cutaneous cases are exceedingly rare and may often be mistaken as something else. Factor XIIIa is often used as a marker to facilitate diagnosis of dermatofibroma. Our case shows that PEComa can exhibit non-specific immunoreactivity for Factor XIIIa; as subtotal biopsies from PEComa can bear some histologic resemblance to those of a lipidized dermatofibroma. It is important to be aware of this potential immunohistochemical diagnostic pitfall.

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