Aberrant Expression of FLI-1 in Melanoma

Abstract

FLI-1 (Friend leukemia integration site 1) nuclear transcription factor has been proposed as a suitable tool in the differential diagnosis of small round cell sarcomas. It has also been described as nuclear marker of endothelial differentiation. Expression of FLI-1 has been demonstrated in Ewing's sarcoma/ primitive neuroectodermal tumor (ES/PNET) and vascular neoplasms. In the present study, we describe two cases of metastatic melanoma with small round blue cell morphology that showed strong nuclear expression of FLI-1. Because of the small round blue cell morphology and negative immunohistochemical staining for pan-melanocytic cocktail (HMB45, anti MART1 and anti-tyrosinase) and SOX10 in both cases, FLI-1 immunostaining was requested as part of the tumors workup. FLI-1 was strongly positive in both cases. Ultimately, both cases were established as being metastatic melanoma. Dermatopathologists should be aware that melanoma can be strongly positive for FLI-1 and not to mistake these cases for ES/PNET or vascular lesions, especially in those cases with unusual morphology.

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