The uterus is a female reproductive organ that has two parts: the lining, called the endometrium; and the outer layer of muscle, called the myometrium. While the majority of uterine cancers start in the endometrium, some start in muscles of the uterus or other tissues. Cancers of this organ are called uterine or endometrial cancers.
Uterine Sarcoma
The American Cancer Society defines sarcomas as cancers arising from tissues like bone, muscle, fat and fibrous tissue. Uterine sarcomas start in the muscle of the uterus or the muscles that surround the uterus, according to the National Cancer Institute. Uterine sarcomas comprise a minimal percentage of uterine cancers, and are grouped into two main groups: endometrial stromal sarcomas, which start in supporting connective tissue of the uterus; and uterine leimyosarcomas that start in the wall of the uterus. They make up approximately 1 percent and 2 percent of uterine cancers, respectively. Survival rates for leiomyosarcoma are worse than those for endometrial stromal sarcoma.
Endometrial Carcinomas
The endometrium is the lining of the uterus, and cancer that starts in the cells of this lining is called endometrial carcinoma. Cancers that start in the cells that form glands are called adenocarcinomas. The most common kind of carcinoma is endometrioid adenocarcinoma, making up 80 percent of endometrial cancers. Other kinds are clear cell adenocarcinoma, serous carcinoma and poorly differentiated carcinoma.
Uterine carcinosarcoma
Uterine carcinosarcoma starts in the uterus and when looked at microscopically, the cells have characteristics of both carcinoma and sarcoma. They are also called malignant mixed müllerian tumors (MMMT), and comprise approximately 4 percent of uterine cancers. Uterine carcinosarcomas have a slightly worse prognosis compared to uterine carcinomas, according to the American Cancer Society.
