Pigmented atypical fibroxanthoma.

ABSTRACT

AIM: The purpose of this report is to call attention to a pigmented variant of atypical fibroxanthoma that resembles malignant melanoma, both clinically and histopathologically. METHODS AND RESULTS: Thirty-eight cases of atypical fibroxanthoma were examined for the presence of pigmented areas. Four such cases were found. Neoplastic cells showed erythrophagocytosis and accumulation of haemosiderin pigment in the cytoplasm. In three cases, immunohistochemical studies using a battery of antibodies were performed. Neoplastic cells were strongly positive for vimentin and weakly positive for CD68, whereas they were negative for melanocytic markers, including S100 protein, HMB45, and the monoclonal antibody NK1-C3 to melanoma-associated antigen. CONCLUSIONS: Pigmented atypical fibroxanthoma represents a poorly recognized variant of the neoplasm that may be easily misinterpreted as malignant melanoma. To the best of our knowledge, this is the first report of erythrophagocytosis in atypical fibroxanthoma.