Pigmented atypical fibroxanthoma: a tumor that may be easily mistaken for malignant melanoma.

Nine cases of an unusual presentation of atypical fibroxanthoma that we previously termed pigmented atypical fibroxanthoma are reported. Pigmented atypical fibroxanthoma can be easily mistaken for malignant melanoma both clinically and histopathologically. The resemblance of pigmented atypical fibroxanthoma to melanoma is secondary to the ability of neoplastic cells to ingest and degrade erythrocytes following intratumoral hemorrhage and to accumulate hemosiderin in their cytoplasm. The histopathologic diagnosis of pigmented atypical fibroxanthoma can be easily confirmed by immunohistochemistry and iron stain.