What Is Endometrial Cancer?

Endometrial cancer starts in the lining (endometrium) of the womb (uterus). The uterus is a hollow organ shaped like a pear that is located in the pelvis between the bladder and the rectum. The uterus is part of a woman’s reproductive system and is where a baby grows during pregnancy. Endometrial cancer is also known as uterine cancer and uterine adenocarcinoma.

Uterine cancer begins when cells in the uterus begin to grow and divide without stopping. These cells clump together to form lumps (masses), called tumors. Cancerous tumor cells can spread to other parts of the body if they are not treated and eliminated.

Endometrial cancer is one of the most common cancers in women in the United States. About 42,160 women will be diagnosed with endometrial cancer in the United States in 2009, according to the American Cancer Society.  

The Uterus

The uterus is part of a woman’s reproductive system. It has several parts:

• Cervix - Narrow lower part of the uterus that connects the uterus to the vagina.
• Corpus (body of the uterus) - Broad middle part of the uterus. The corpus wall has three layers of tissue:
  
  • Endometrium - Inner layer or lining.
  • Myometrium - Thick layer of muscle in the middle layer that pushes the baby out during birth.
  • Serosa - Outer layer of the upper part of the uterus.
    
• Fundus - Dome-shaped top of the uterus.

On each side of the uterus, there is one fallopian tube and one ovary, where the eggs are formed. Eggs pass from the ovaries to the uterus through the two fallopian tubes.

Every month until you reach menopause (when you stop having monthly periods), the lining of your uterus grows and thickens so that it is ready to accept a fertilized egg if you become pregnant. If you do not get pregnant, the thick, bloody lining of your uterus passes out of your body through your vagina during your monthly period (menstruation). This cycle continues until you reach menopause.

How Endometrial Cancer Starts

Endometrial cancer begins when cells in the uterus begin to grow and divide without stopping. These cells join together to form lumps (masses) called tumors. Some of these tumors are not cancerous (benign). Benign conditions of the uterus include noncancerous tumors in the muscle of the uterus (fibroids) and an increased number of cells in the uterine lining (endometrial hyperplasia).

Other tumors in the uterus are cancerous (malignant). They are usually more serious than benign tumors and can be life threatening. Cancer cells can invade and damage nearby tissues and organs. They can also break away from a tumor, enter the bloodstream, and settle in other organs in the body. This is called metastasis. The cancer cells may also spread to the lymphatic system. In this way, cancer cells can spread (metastasize) from the original (primary) tumor to form new tumors in the lymph nodes (small bean-shaped organs that help fight infection) and other organs.

When cancer spreads from its starting place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if endometrial cancer spreads to the lungs, the cancer cells in the lungs are endometrial cancer cells and the disease is metastatic endometrial cancer, not lung cancer. Doctors sometimes call the new tumor "distant" metastasis.

Types of Uterine Cancer

The most common kinds of uterine cancer are:

• Adenocarcinoma - Almost all uterine cancers (about 95 percent) are adenocarcinomas. Adenocarcinomas start in the lining, or endometrium, of the uterus. There are two types of endometrial adenocarcinomas:
  
  
  • Endometrioid adenocarcinoma - The cancer looks like the normal tissue that lines the endometrium. This kind of cancer does not usually spread to other tissues, so it is not very dangerous. About 75 percent of cancers of the uterus are endometrioid adenocarcinomas.
  • Papillary serous adenocarcinoma and clear-cell adenocarcinoma - This type of cancer does not look like the normal lining of the endometrium. Papillary serous adenocarcinoma and clear-cell adenocarcinoma often spread, so they are more dangerous than endometrioid adenocarcinoma. About 10 percent of endometrial cancers are papillary serous adenocarcinomas and 5 percent are clear-cell adenocarcinomas.
    
    
• Uterine sarcoma - Uterine sarcoma starts in the muscle, or myometrium, of the uterus. Information on uterine sarcoma is available in the section on soft-tissue sarcoma. The rest of this document focuses only on endometrial adenocarcinoma.
  

Key Statistics

According to the American Cancer Society, endometrial cancer is most common in women between 45 and 74 years of age; only 8 percent of these cancers occur in women younger than 45. A woman’s chance of being diagnosed with endometrial cancer during her lifetime is 1 in 41. Endometrial cancer is 40 percent more common in white women than African-American women.

This content has been reviewed and approved by Myo Thant, MD.