Myxoid Pleomorphic Fibroma

Abstract

A 77‐year‐old white female presented with a two to three year history of an asymptomatic skin‐colored papule on the right upper arm. Examination revealed a 7 mm × 7 mm soft papule, supplanted by a smaller soft papule. Clinical differential diagnosis included an adnexal tumor, neurofibroma, and dermal nevus. Histological examination revealed a sparse proliferation of spindle and stellate‐shaped cells within the dermis, including many large cells with bizarre shaped nuclei. Focal multinucleated giant cells were present as well. The background stroma was both collagenous and myxoid, the later being highlighted by diffuse colloidal iron staining. The spindle and stellate‐shaped cells demonstrated CD34 and vimentin positivity. Factor XIIIa was focally positive. Actin and S‐100 staining were negative. These changes were thought to be consistent with a myxoid pleomorphic fibroma. This is a rare tumor, with only a few reported cases of myxoid variants in the literature to date. The staining pattern of this tumor, along with others in the reported literature, suggest a mesenchymal, fibroblastic origin.