Recurrent Leiomyosarcoma of the Skin

Abstract

Leiomyosarcoma arising at any site is a relatively uncommon tumor and accounts for 10% to 15% of limb sarcomas. Superficial leiomyosarcoma is much less common, comprising approximately 2%–6% of sarcomas. These are divided into 2 distinct forms, dermal and subcutaneous. Dermal leiomyosarcomas, thought to arise from the arrector pili muscles, have a diffuse growth pattern with ill-defined borders and may extend downward into the subcutaneous tissue. Subcutaneous leiomyosarcomas, thought to arise from the smooth muscle of vessel walls, may have either a nodular or a diffuse growth pattern and may extend upward into the lower dermis. Both forms recur locally in up to 70% of patients, usually within 5 years of the primary excision. Dermal leiomyosarcomas have a lower recurrence rate than subcutaneous lesions. Recurrences tend to be more atypical and more deeply located than the orig-inal lesion. Subcutaneous leiomyosarcomas metastasize in up to 30%–40% of cases, most frequently to the lungs. Metastasis from dermal leiomyosarcomas is rare. There are no distinctive clinical features, and the diagnosis is usually made on histologic examination. While there are often morphologic clues to the smooth muscle origin of the tumor, the differential diagnosis from other dermally based spindle-cell tumors may be problematic. A variety of benign and malignant spindle-cell neoplasms may have similar features, but the primary differential diagnosis of superficial leiomyosarcoma is from spindle-cell or desmoplastic melanoma, spindle-cell squamous carcinoma, and atypical fibroxanthoma. Accurate diagnosis may require the use of multiple immunohistochemical stains in conjunction with routine histologic evaluation.