Primary cutaneous leiomyosarcoma. A histological and immunohistochemical study of 9 cases, with ultrastructural correlation.

Leiomyosarcoma (LMS) of dermal and subcutaneous tissues is an uncommon neoplasm. In order to analyze the specialized pathologic features of this tumor, we undertook a histological, ultrastructural, and immunohistochemical study of 9 superficial LMS, including 7 dermal lesions and 2 subcutaneous neoplasms. These were compared with 12 examples of "deep" extracutaneous LMS. Metastases to the skin from two of the latter neoplasms were also examined. Immunohistochemistry was found to be a useful diagnostic adjunct to light microscopic and ultrastructural studies in that all LMS coexpressed vimentin and desmin, regardless of site, and 90% also expressed muscle-specific actin. Variable expression of cathepsin B and myelin basic protein was noted in 8 and 10 tumors, respectively, whereas none contained cytokeratin. Weak cytoplasmic positivity for epithelial membrane antigen was seen in 1 dermal and 3 extracutaneous LMS. Of 7 dermal LMS, 4 contained S-100 protein, whereas this determinant was found in only 1 of 12 extracutaneous tumors. Conversely, Leu 7 reactivity was present in 7 of 12 extracutaneous LMS, but only 2 of 9 superficial lesions. Review of clinical features confirmed that subcutaneous LMS is capable of aggressive behaviour, whereas dermal LMS was more likely to behave in an indolent fashion. However, one example of dermal LMS exhibited aggressive local recurrences and distant metastasis, ultimately leading to the death of the patient. Therefore, careful clinical followup is indicated in all cases.