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Case Reports

Abstract

Aneurysmal fibrous histiocytoma (AFH) is a rare variant of fibrous histiocytoma (FH) characterized by its distinct histopathological features and clinical presentation, notorious for its propensity to be mistaken for melanocytic or vascular neoplasms. PRKCD gene rearrangements including CD63::PRKCD have been described in conventional FH but only LAMTOR1::PRKCD gene fusion has been reported in AFH. Herein, we report a case of AFH with CD63::PRKCD in a 20-year-old female presenting with a right thigh mass.

Histopathologic examination revealed a dermal-based proliferative lesion composed of bland fusiform cells, mononuclear cells, and multinucleate arranged in a storiform growth pattern, admixed with areas showing prominent cleft-like and cavernous spaces containing blood elements. The periphery of the lesion showed collagen trapping with xanthomatous areas. By immunohistochemistry, the lesional cells were positive for vimentin, multifocal positivity for FXIIIa, and focal positivity for CD34 (at the interface of the lesional cells and subcutis), and negative for other markers including Smooth Muscle Actin, Desmin, MART1, S100, SOX10, CK7, CK20, CK5/14, and p63 were negative. The Ki-67 proliferative index was low (<1%). RNA-Seq fusion panel revealed a CD63::PRKCD fusion. No mutations were detected on the solid tumor NGS panel. Taken together, these findings confirm the diagnosis of AFH.

In summary, we report a rare occurrence of CD63::PRKCD gene fusion in a case of cutaneous AFH. Our case along with other cases of AFH in precedent literature, supports a diagnostic role of PRKCD gene rearrangement by fluorescence in situ hybridization, particularly in limited and/or challenging biopsy specimens.