Atypical fibroxanthoma/pleomorphic dermal sarcoma of the scalp with aberrant expression of HMB-45: a pitfall in dermatopathology

Atypical fibroxanthoma (AFX) has been considered as the non-infiltrating precursor lesion of pleomorphic dermal sarcoma (PDS), which shows an aggressive clinical behavior, because of its extensive invasion of the deeper skin layers. Although these two tumors may represent two stages of the same disease, it can be difficult to differentiate between them, because of their similar clinical and histological features 1. Furthermore, they must be distinguished from a spindled variant of squamous carcinoma, melanoma and leiomyosarcoma 2. AFX/PDS still remains a diagnosis of exclusion, that needs to combine immunohistochemical markers for a definitive diagnosis. Usually AFX/PDS shows positivity for CD10, CD99, CD68, vimentin and lysozyme, while S100, HMB45, MART-1, cytokeratins, CD34, CD31, desmin and h-caldesmon are absent.