Pleomorphic Dermal Sarcoma: A Clinical and Histopathologic Emulator of Atypical Fibroxanthoma, but Different Biologic Behavior

Description Pleomorphic dermal sarcoma (PDS) can clinically and histopathologically mimic atypical fibroxanthoma (AFX). However, it has a more aggressive clinical course with a higher recurrence rate and metastatic potential. This case presentation aims to report a rapidly-growing, exophytic, 4 cm tumor following a non-diagnostic shave biopsy 2 months prior and to highlight distinctive features between PDS and AFX needed to make the correct diagnosis. Like AFX, PDS occurs on the sun-damaged skin of the elderly, usually on the head and neck. Also, like AFX, PDS histopathologically consists of sheets or fascicles of epithelioid and/or spindle-shaped cells, often with multinucleation, pleomorphism, and numerous mitotic figures. Immunohistochemistry cannot distinguish PDS from AFX but is used to exclude other malignancies. PDS can be distinguished from AFX by size (PDS is usually >2.0 cm) and by the presence of more aggressive histopathologic features, such as subcutaneous involvement, perineural and/or lymphovascular invasion, and necrosis. PDS is a rare entity not well documented in the literature with confusing, misleading, and changing nomenclature. PDS is a diagnosis of exclusion made after complete excision of the tumor with the aid of histopathology and immunohistochemistry.