Cancer occurs when cells in an area of the body grow abnormally. The endometrium is the lining layer of the uterine cavity where most uterine cancers begin because of cancerous changes in the lining. In the most common type of uterine cancer, endometrial cancer, cells in the endometrial lining grow out of control, may invade the muscle of the uterus and sometimes spreads outside of the uterus (ovaries, lymph nodes, abdomen).
Uterine sarcomas are a type of uterine cancer in which malignant cells form in the muscle of the uterus (leiomyoscarcoma) or in the network of support cells in the uterine lining (stromal sarcomas and carcinosarcomas). Only about 5% of uterine cancers are uterine sarcomas, but they tend to have more aggressive clinical behavior and can spread quickly.
The Foundation for Women’s Cancer offers educational materials that explore this in more depth.