A uterine leiomyosarcoma is a rare malignant (cancerous) tumor that arises from the smooth muscle lining the walls of the uterus (myometrium). There are essentially two types of muscles in the body: voluntary and involuntary. Smooth muscles are involuntary muscles; the brain has no conscious control over them. Smooth muscles react involuntarily in response to various stimuli. For example, the myometrium stretches during pregnancy to help accommodate the fetus and contracts during labor to help push out a baby during childbirth.
Leiomyosarcoma is a form of cancer. The term "cancer" refers to a group of diseases characterized by abnormal, uncontrolled cellular growth that invades surrounding tissues and may spread (metastasize) to distant bodily tissues or organs via the bloodstream, the lymphatic system, or other means. Different forms of cancer, including leiomyosarcomas, may be classified based upon the cell type involved, the specific nature of the malignancy, and the disease's clinical course.
Leiomyosarcoma is classified as a soft tissue sarcoma. Sarcomas are malignant tumors that arise from the connective tissue, which connects, supports and surrounds various structures and organs in the body. Soft tissue includes fat, muscle, never, tendons, tissue surrounding the joints (synovial tissue), and blood and lymph vessels. The exact cause of leiomyosarcoma, including uterine leiomyosarcoma, is unknown.