There are two general categories of tumors, pure and mixed. If there are between 5 to 10 dividing cells, they are considered a low-grade malignancy. These are known as mixed mesodermal sarcomas, and are further subdivided into homologous and heterologous tumors. The heterologous type contain cellular elements not normally found in the uterus, including malignant bone, fat, cartilage and striated muscle. Heterologous mixed mesodermal tumors are the most common type of uterine sarcoma and account for 1 to 3 percent of all uterine cancers.
Homologous tumors are much less common.
How It Spreads Uterine sarcomas can grow locally to involve the tissue surrounding the uterus and cervix, to the rectum and bladder, to the groin, pelvic and aortic lymph nodes, to the surfaces of the abdominal cavity and distantly to the liver, lung, and brain. Leiomyosarcomas spread by direct local extension, abdominal implantation or via the bloodstream. The lung is the most common site of metastases, followed by the liver, brain and bone. Low-grade stromal sarcomas are usually slow growing and tend to remain confined to the uterus in about 70 percent of cases. Spread beyond the uterus occurs via the lymph system or via the bloodstream.