Primary leiomyosarcoma of skin: a report and critical appraisal.

A primary leiomyosarcoma of skin was studied by light and electron microscopy and by histochemistry. Systematic evaluation of the entire neoplasm suggested that a single biopsy sample would show little cellular pleomorphism but could vary considerably in number of mitoses per mm2. Electron microscopy revealed a high degree of cytologic differentiation. Strong myosin ATPase activity and negative demonstrations for hydrolytic enzymes suggest a diagnostic profile which will clearly separate this neoplasm from malignant fibrous histiocytoma. High mitoses counts, the conventional criterion for malignancy of non-cutaneous smooth muscle tumors, may not be appropriately applied to primary leiomyosarcomas arising in the dermis. The findings in this case and a critical review of the literature suggest that reliable criteria for diagnosis of primary cutaneous leiomyosarcoma by light microscopy remain to be established.