Superficial acral fibromyxoma and other slow-growing tumors in acral areas.

Superficial acral fibromyxoma (SAFM) is a rare fibromyxoid mesenchymal tumor with a predilection for the distal extremities and frequent nail bed involvement. Superficial acral fibromyxoma typically arises as a solitary, slow-growing nodule on a toe or finger, with the great toe being the most commonly affected site. Histopathologically, SAFM characteristically presents as a well-circumscribed but unencapsulated dermal tumor composed of spindle and stellate cells in a loose storiform or fascicular arrangement embedded in a myxoid, myxocollagenous, or collagenous stroma. The tumor often occupies the entire dermis and may extend into the subcutis and occasionally the underlying fascia and bone. The characteristic immunohistochemical profile of SAFM includes expression of CD34, epithelial membrane antigen (EMA), and CD99; it is notably negative for S-100 protein. We report 3 cases of SAFM and also provide a review of the literature on the clinical and histopathologic presentations of this unique entity as well as the differential diagnosis.