The uterus is pear shaped with the narrow end pointing down. This narrow lower end, which extends into the vagina, is the cervix. The wider upper part is the body of the uterus, or the uterine corpus.
There are three layers to the body of the uterus:
- Endometrium, the inner lining
- Myometrium, a thick layer of muscle
- Serosa, the outer covering, or membrane
Connective tissue called stroma supports the other uterine tissues.
What is Uterine Sarcoma?
Most cancer in the uterus—more than 95 percent—starts in the endometrium. This is called endometrial cancer or endometrial carcinoma. (“Carcinoma” is the term for cancer that starts in one of the body’s linings or membranes.) We discuss endometrial cancer in its own section of the website.
In rare cases, cancer starts in another tissue of the uterus. Most of these cancers are uterine sarcoma. (“Sarcoma” is the term for cancer that starts not in a body lining but in one of the body’s other tissues, like muscle, bone, fat, or fibrous tissue.) Only about 3% of uterine cancers are uterine sarcoma. Other less common uterine cancers are uterine papillary serous carcinoma, clear cell carcinoma, and carcinosarcoma (also called malignant mixed mesodermal tumors or malignant mixed mullerian tumors).
Uterine sarcoma occurs when cells in the body of the uterus, usually in the muscle layer, begin to grow abnormally. These cells do not respond to regular cell growth, division, and death signals like they are supposed to. They also don’t organize normally. Instead they grow into a tumor, which may break through into other layers of the uterus.
Although the cervix is part of the uterus, cancer that starts in the cervix is referred to as cervical cancer, and it’s discussed in its own section of this website.
This rest of this section is about uterine sarcoma.
Types of Uterine Sarcoma
About 1,400 new cases of uterine sarcoma are diagnosed each year in this country. The three types of uterine sarcoma are:
- Uterine leiomyosarcoma, the most common type, which starts in the myometrium
- Endometrial stromal sarcoma, a rare type, which starts in the connective tissue that supports the endometrium (endometrial stroma)
- Undifferentiated sarcoma, a rare type, which is similar to endometrial stromal sarcoma but more aggressive, meaning it grows and spreads more quickly