Superficial acral fibromyxoma: A clinicopathologic and immunohistochemicalanalysis of 37 cases of a distinctive soft tissue tumor with a predilection for the fingers and toes

This report describes the clinicopathologic features and immunohistochemica l findings identified in 37 cases of a distinctive soft tissue tumor that h as a predilection for the hands and feet. The study group included 25 male and 12 female subjects ranging in age from 14 to 72 (mean, 43; median, 46) years. The patients presented with solitary masses 0.6 to 5.0 cm (mean, 1.7 5 cm) that were present from 3 months to 30 years (median duration, approxi mately 3 years) before surgical intervention and involved the toes (n = 20) , fingers (n = 13), and palm (n = 4). Twenty of the cases were documented t o involve the nail region. Histologically, the tumors were typically locate d in the dermis or subcutis and composed of spindled and stellate-shaped ce lls with random, loose storiform, and fascicular growth patterns. The lesio nal cells were embedded in myxoid or collagenous, matrix, often with mildly to moderately accentuated vasculature and increased numbers of mast cells. There was generally slight to mild nuclear atypia; only 3 cases had more s ubstantial atypia. Mitotic figures were infrequent. Occasional multinucleat ed stromal cells were noted in 19 cases. The process showed immunoreactivit y for CD34 (21 of 23 cases), epithelial membrane antigen (18 of 25 cases), and CD99 (11 of 13 cases). No immunoreactivity was detected for actins, des min, keratins, or HMM-45, and only 1 of 23 tumors had weak reactivity for S 100 protein. The surgical specimens consisted of biopsy or partial resectio n specimens (n = 4), local excisions (n = 29), and amputated or partially a mputated digits (n = 4). Detailed follow-up, available for IS patients (mea n follow-up interval, 10.1 years), revealed I recurrence after local excisi on and 2 instances of persistent or progressive disease after partial excis ion. A differential diagnosis of fibrous histiocytoma, dermatofibrosarcoma protuberans, acquired (digital) fibrokeratoma, sclerosing perineurioma, cut aneous myxoma (,superficial angiomyxoma), and acral myxoinflammatory fibrob lastic sarcoma is discussed. HUM PATHOL 32:704-714. This is a US government work. There are no restrictions on its use.