Superficial acral fibromyxoma: report of 4 cases with CD10 expression and lipomatous component, two previously underrecognized features.

Superficial acral fibromyxoma (SAF) is an uncommon tumor of the superficial soft tissues of acral extremities in middle-aged adults, firstly described in a series of 37 cases by Fetsch et al. in 2001. Since then, just a few case reports have been published. It is histologically characterized by a slightly to moderately cellular proliferation of spindled and stellate-shaped bland fibroblastic cells, arranged in a random, loose storiform, or fascicular growth pattern, within a myxoid, myxocollagenous, or collagenous stroma, with a prominent vasculature. The cells express CD34, CD99, and, frequently, epithelial membrane antigen. We report 4 cases that show clinical, morphological, and immunohistochemical characteristics of SAF and, additionally, exhibit two features rarely documented in previous publications, such as CD10 expression and a lipomatous component. Three of our 4 cases express CD10. The single previously reported case tested for CD10 was also positive. One of our cases contains mature fat cells intermingled with the spindle cells throughout the lesion. This finding has not been documented before in SAF. Our small series shows that SAF frequently expresses CD10 and occasionally can have a lipomatous component.