Subungual Acral Fibromyxoma Involving the Bone: A Mimicker of Malignancy.

Superficial acral fibromyxoma (SAF) is a recently recognized myxoid tumor that usually occurs on the fingers and toes of middle-aged adults. We report the case of a 53-year-old man with a SAF on the first left toe that had been slowly growing for 2 years. Hispathologically, the lesion was nonencapsulated and was composed of stellate and spindle cells, arranged in a myxoid matrix. No atypia or mitotic figures were found. Neoplastic cells showed positive staining for CD34 and negative staining for epithelial membrane antigen, actin, desmin, keratins, S-100 protein, and HMB45. Main differential diagnoses of SAF include benign and malignant myxoid and spindle cells tumors, such as myxoid fibrous histiocytoma, superficial angiomyxoma, myxoid neurofibroma, myxoid dermatofibrosarcoma protuberans, and low-grade fibromyxoid sarcoma.