Superficial acral fibromyxoma: report of two cases

Superficial acral fibromyxoma (SAFM) is a rare soft tissue tumor that has recently been delineated as a separate entity. We report 2 cases of SAFM and discuss its pathological features and differential diagnosis. Both patients had lesions on the toe. In 1 patient, the tumor was found after nail extraction, which had been performed for the treatment of onychomycosis, whereas in the other patient the tumor itself was the reason for seeking dermatological assistance. Biopsies from both cases demonstrated similar features. There was a moderately circumscribed, non-encapsulated tumor extending through the whole dermis. The neoplasm was composed of spindle and stellate cells with slight nuclear atypia arranged in a loose storiform, partly fascicular growth pattern. In 1 case, strands of cells with rather wavy nuclei were seen at the periphery of the tumor. Mitotic figures were scarce. The neoplastic cells were embedded in a myxoid stroma with increased numbers of small blood vessels and scattered mast cells. Immunohistochemically, the tumor cells showed weak focal positivity for CD34 and stained negatively for S-100 protein and alpha-smooth muscle actin. In 1 case epithelial membrane antigen (EMA) was negative, whereas in the second case focal expression of EMA by neoplastic cells was seen. Alcian blue staining revealed abundant mucinous material within the stroma. In conclusion, SAFM represents a distinct entity in the spectrum of cutaneous myxoid tumors. The differential diagnosis of SAFM includes various myxoid neoplasms and tumors with a predilection for distal parts of the extremities.