Within the soft tissue, cutaneous and subcutaneous leiomyosarcomas occur most commonly. Superficial leiomyosarcomas are usually divided into the two subcategories of cutaneous and subcutaneous leiomyosarcomas due not only to their difference in location, but also due to their differences in prognosis and their likely site of origin. Cutaneous leiomyosarcomas, the type presented in this case, are believed to derive from precursor cells associated with the arrector muscles of the hair, the smooth muscle surrounding sweat glands or the genital dartos muscle. The majority occur between 40 and 60 years of age and occur more frequently in males. Cutaneous leiomyosarcomas often present as a solitary nodule smaller than 2cm, usually on the extremities, particularly on the hairbearing extensor surfaces and on the lower extremities.
Some patients are even asymptomatic.
However, metastatic leiomyosarcomas may exhibit prominent atypia. The proliferating cells are arranged in cellular poorly circumscribed fascicles of spindle cells with elongated nuclei with blunt ends and inconspicuous nucleoli. Identification of the smooth muscle may be facilitated with a Masson's trichrome stain or a phosphotungstic acid-hematoxylin stain. The vast majority of these lesions are desmin, muscle specific actin, and vimentin positive. Generally, cutaneous leiomyosarcomas are associated with a good prognosis.