Another 15 percent of uterine sarcomas arise from the supporting stromal cells that surround the glands within the lining of the uterus (the endometrium) and are known as pure endometrial stromal sarcomas. They are classified according to grade, from the less virulent low-grade tumors to the extremely virulent high-grade tumors.
The most common type of uterine sarcomasóhalf of all casesóarise from both the endometrial glands and the supporting stromal cells of the endometrium. These are known as mixed mesodermal sarcomas, and are further subdivided into homologous and heterologous tumors. The homologous varietyóalso known as carcinosarcomasócontain malignant cells transformed from cells normally found in the uterus. The heterologous typeócalled malignant mixed mesodermal tumorsó 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 ( see "Cancers of Female Pelvic Organs" ).
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.
