CASE AND RESEARCH LETTERS Superficial Acral Fibromyxoma: A CD34 Periungual Tumor

We report on the case of a 40-year-old patient, with no relevant medical history, who consulted for a periungual tumor on the second finger of the left hand. The lesion, which was asymptomatic, had appeared 2 years earlier, and had shown slow, progressive growth. The physical examination showed a 1-cm diameter tumor with poorly defined borders that was not attached to the deep layers (Fig. 1A). The lesion was firm and slightly painful on palpation. Four years earlier, a similar lesion----diagnosed as periungual fibroma----had been excised from the same location. Histologic examination of the current lesion, removed by simple excision with curettage of the base, showed an epidermis with mild orthokeratotic hyperkeratosis and a poorly circumscribed dermal neoplasm (Fig. 1B) formed by a population of spindle cells embedded in loose stroma composed of alternating myxoid and fibromyxoid areas of identical cell density, without a clearly defined architecture (Fig. 1C). There were also numerous mast cells that stained positive for CD117. Alcian blue staining showed a predominance of acid mucopolysaccharides in less fibrous areas. There was no evidence of nuclear atypia or mitosis. Neoplastic cells were diffusely and strongly positive for CD34 (Fig. 1D) and CD99 throughout the thickness of the tumor, and there was a low Ki-67 index (<5%). Staining for epithelial membrane antigen (EMA) and S100 protein was negative. Based on these findings, a diagnosis of superficial acral fibromyxoma (SAF) was established. Because the lateral and deep borders of the resection specimen were affected, extension of the surgical field was considered, but the patient refused a second operation. He has attended regular follow-up visits, and at the time of writing, 6 months later, he remains asymptomatic. Magnetic resonance imaging at the 4-month follow-up showed no evidence of residual tumor.