Fibroma-like PEComa: A Tuberous Sclerosis Complex-related Lesion

Perivascular epithelioid cell tumor (PEComa), mesenchymal tumors morphologically characterized by epithelioid cells, coexpress melanocytic and muscle markers. Herein, we describe a heretofore-undescribed tuberous sclerosis complex (TSC)-related neoplasm, morphologically resembling a soft tissue fibroma-like lesion, but showing an immunophenotype resembling PEComa. We identified 3 soft tissue fibroma-like lesions in individuals with TSC. We also evaluated 6 TSC-related periungual fibroma as well as a range of non-TSC fibroma-like lesions (n=19). Immunohistochemistry for HMB-45, desmin, smooth muscle actin, TFE3, and S100 was performed on the TSC-related fibromas. Periungual fibromas and non-TSC fibroma-like lesions were also stained for HMB-45. All 3 TSC patients were female, ranging in age from 4 to 51 years (mean, 26.7 y). Two tumors were located in extremities and 1 on the chest wall. The tumors showed elongated to stellate spindle-shape cells, prominent collagenous background, and lacked mitotic activity and cytologic atypia. Immunohistochemically, all 3 tumors were positive for HMB-45; smooth muscle actin or desmin was positive in both tumors tested. TFE3 was negative. All patients were alive with no evidence of disease with median follow-up of 55 months (range, 6 to 131 mo). Non-TSC fibroma-like lesions and oral and periungual fibromas were negative for HMB-45. Fibroma-like PEComa, a newly recognized soft tissue tumor with a strong association with TSC, mimics soft tissue fibroma but shows reactivity with melanocytic markers.