Leiomyosarcoma is a malignant soft tissue tumor of muscle involving the smooth muscle of blood vessels or organ walls. Leiomyosarcoma is a high grade soft tissue sarcoma that usually penetrates beyond its compartment (stage IIB). It usually occurs in adults, especially women. The most common site is the abdomen (retroperitoneum). Leiomyosarcomas are classified by their location: retroperitoneum, subcutaneous skin, blood vessels or extremities. Treatment is surgical excision with or without radiation, and occasionally chemotherapy.