Uterine sarcoma is a cancer of the muscle and supporting tissues of the uterus (womb).

About the uterus

The uterus is a hollow organ, about the size and shape of a medium-sized pear. It has two main parts. The lower end of the uterus, which extends into the vagina, is called the cervix. The upper part of the uterus is called the body, and is also known as the corpus. The body of the uterus has 3 layers. The inner layer or lining is called the endometrium. The serosa is the layer of tissue coating the outside of the uterus. In the middle is a thick layer of muscle that is also known as the myometrium. This muscle layer is needed to push the baby out during birth.

Cancers of the uterus and endometrium

Sarcomas are cancers that start from tissues such as muscle, fat, bone, and fibrous tissue (the material that forms tendons and ligaments). Cancers that start in epithelial cells, the cells that line or cover most organs, are called carcinomas.

More than 95% of cancers of the uterus are carcinomas. If a carcinoma starts in the cervix, it is called a cervical carcinoma. Carcinomas starting in the endometrium, the lining of the uterus, are called endometrial carcinomas. These 2 cancers are discussed in our documents Cervical Cancer and Endometrial Cancer. This document is about uterine sarcomas.

Most uterine sarcomas fall into 1 of 2 categories, based on the type of cell they developed from:

• Endometrial stromal sarcomas develop in the supporting connective tissue (stroma) of the endometrium. These cancers are rare, representing a little over 1% of all uterine cancers. These tumors can be divided into 2 groups: low-grade and undifferentiated (high-grade). Low-grade endometrial stromal sarcomas tend to grow slowly - patients with these tumors have a better outlook than those with undifferentiated (high grade) tumors. Undifferentiated tumors are more aggressive and respond differently to treatment than low-grade tumors.

• Uterine leiomyosarcomas start in the muscular wall of the uterus known as the myometrium. These tumors make up about 2% of cancers that start in the uterus.

Another type of cancer that starts in the uterus is called carcinosarcoma. These cancers start in the endometrium and have features of both sarcomas and carcinomas. They can be classified with uterine sarcomas, but many doctors believe they are more closely related to carcinomas. These cancers are also known as malignant mixed mesodermal tumors or malignant mixed mullerian tumors. Uterine carcinosarcomas are discussed in detail in the American Cancer Society document about endometrial cancer.

Benign tumors

Several types of benign (non-cancerous) tumors can also develop in the connective tissues of the uterus. These tumors, such as leiomyomas, adenofibromas, and adenomyomas, are also known as fibroid tumors. Most of the time, these tumors require no treatment. Treatment may be needed, however, if they start causing problems - such as pelvic pain, heavy bleeding, frequent urination, or constipation. In some cases, the tumor is removed, leaving the rest of the uterus in place; this surgery is called myomectomy. Some treatments can destroy these benign tumors without surgery, by blocking the blood vessels that feed them, by killing the tumor cells with electric current, or by freezing them with liquid nitrogen. Another option is to remove the entire uterus (surgery called a hysterectomy). The rest of this document is about uterine sarcomas.

Last Medical Review: 11/18/2009
Last Revised: 11/18/2009