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Low-grade fibromyxoid sarcoma (LGFMS), usually a deeply situated mass in adults, is uncommon in superficial soft tissue and in children. Nineteen superficial LGFMS from our files were studied for clinicopathologic features, the latter including tumor size, growth pattern, cellularity, collagen rosettes, vascularity, nuclear atypia, mitotic rate, necrosis, and immunophenotype. The patients included 12 males and 7 females who ranged in age from 2 to 70 years (mean, 29 years). There were 7 children. Tumor locations included the lower extremity (8), buttock (3), trunk (3), vulva/inguinal region (2), upper extremity (2), and unspecified subcutis (1). Clinical and histologic submitting diagnoses were mainly benign except for 3 cases, submitted as low-grade sarcoma, with only one as superficial LGFMS. The mean tumor size was 4.2 cm (range, 1.6-18 cm). Of 15 with evaluable resections, 5 had focal ink on tumor and 2 of these had known negative wider reexcisions. The tumors were relatively well circumscribed with low to moderate cellularity. The tumors alternated from myxoid zones with prominent curvilinear vasculature to collagenous fascicular zones. Collagen rosettes with peripheral round epithelioid cells and focal ischemic necrosis were present in 6 cases each. Mitotic rate was low (mean 1.6/50 HPF). Tumor cells were positive for vimentin and some were focally positive for actins, CD68, and EMA. CD34, keratins, and S-100 protein were negative. Follow-up (mean, 44 months; range, 10-84 months) on 16 patients demonstrated 14 with no evidence for disease, 2 with local recurrences at 5 and 16 months, but no metastases. Superficial LGFMS is more common than previously recognized and may affect children at a higher rate (7 of 19, 37%) than that for deep LGFMS. The prognosis is good and appears to be better than that for deep LGFMS.
Billings et al. (Tue,) studied this question.