Epithelioid leiomyosarcoma of the skin and subcutaneous tissue. Clinicopathologic, immunohistochemical, and ultrastructural study of five cases.

This report describes five cases of an unusual variant of malignant smooth-muscle neoplasm involving the skin and subcutaneous tissue characterized by a proliferation of predominantly round to oval epithelioid cells with abundant eosinophilic cytoplasm. Of the five patients, four were men, one a woman; ages ranged from 69 to 85 years (mean, 76.4). The size of the lesions varied from 1.2 to 2.5 cm; two were located in the scalp, two in the face, and one in the back of the neck. Immunohistochemical evaluation of the tumor cells showed immunoreactivity for actin and vimentin in all cases and negative labeling for desmin, S-100 protein, keratin, epithelial membrane antigen, HMB-45, factor VIII, and alpha-1-antichymotrypsin. Ultrastructural examination showed features of smooth muscle differentiation, that is, focal plasmalemmal densities, basement membrane material, and cytoplasmic filaments with focal condensations. All patients were treated by surgical excision and two also with post-operative radiotherapy. Two cases recurred after 1 year, requiring wide excision. A second recurrence from one of these cases showed the emergence of a highly anaplastic, pleomorphic spindle cell sarcoma; the patient died of unrelated causes, with evidence of persistent disease, after 2 years. In the remainder of cases, the patients were alive and well with no evidence of recurrence or metastasis from 2 to 6 years. Because of the unusual morphologic features of this variant of smooth-muscle tumor it may be confused with a variety of primary and metastatic neoplasms of the skin, including malignant melanoma, epithelioid sarcoma, and metastatic carcinoma. Epithelioid leiomyosarcoma should be recognized as a distinct morphologic variant of primary cutaneous smooth muscle neoplasm and should be considered in the differential diagnosis of epithelioid neoplasms in dermal and superficial soft tissue locations.