Aberrant tyrosinase expression in an atypical fibroxanthoma: a case report

Abstract

Atypical fibroxanthoma (AFX) is a histologic mimicker of a variety of spindle cell neoplasms and careful microscopic and immunohistochemical evaluation is critical in establishing the correct diagnosis. Here we report the histologic and immunohistochemical work-up of a 1 cm nodule involving the left dorsal hand of a 66-year-old patient. Light microscopy revealed fascicles of spindled and pleomorphic cells within the dermis demonstrating increased mitotic activity occurring in the background of sun-damaged skin. There were numerous multinucleated cells with hyperchromatic nuclei and ample finely vacuolated or foamy cytoplasms. There was strong and diffuse CD10 and focal CD68 expression amongst the spindled cells and multinucleated cells. The neoplastic cells did not demonstrate immunoreactivity against S100, p75-NGFR, HMB-45, or a panel of keratinocytic, vascular and smooth muscle markers. Tyrosinase and Melan-A were not expressed within the spindle cell component of this neoplasm, however there was tyrosinase expression amongst numerous multinucleated giant cells. Melan-A expression was also observed among rare multinucleated giant cells. Tyrosinase expression has not previously been reported in AFX.

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