We don't really know what causes endometrial cancer. What's known is that something occurs to create a genetic mutation within cells in the endometrium — the lining of the uterus. The genetic mutation turns normal, healthy cells into abnormal cells. Healthy cells grow and multiply at a set rate, eventually dying at a set time. Abnormal cells grow and multiply out of control, and they don't die at a set time. Cancer cells invade nearby tissues and can separate from an initial tumor to spread elsewhere in the body (metastasize).
Factors that increase the risk of endometrial cancer include:
- Obesity, certain inherited conditions, and taking estrogen alone (without progesterone) can increase the risk of endometrial cancer.
- Taking tamoxifen for breast cancer can increase the risk of endometrial cancer.
- Changes in the balance of female hormones in the body. Your ovaries make two main female hormones — estrogen and progesterone. Fluctuations in the balance of these hormones cause changes in your endometrium.
- A disease or condition that increases the amount of estrogen, but not the level of progesterone, in your body can increase your risk of endometrial cancer. Examples include irregular ovulation patterns, such as can occur in women with polycystic ovary syndrome, obesity and diabetes. Taking hormones after menopause that contain estrogen but not progesterone increases the risk of endometrial cancer.
- Never having been pregnant. Women who have never been pregnant have a higher risk of endometrial cancer than do women who have had at least one pregnancy.
- Older age. As you get older, your risk of endometrial cancer increases. The majority of endometrial cancer occurs in older women who have undergone menopause.
- Obesity. Being obese increases your risk of endometrial cancer. This may occur because excess body fat alters your body's balance of hormones.
- An inherited colon cancer syndrome. Hereditary nonpolyposis colorectal cancer (HNPCC) is a syndrome that increases the risk of colon cancer and other cancers, including endometrial cancer. HNPCC occurs because of a gene mutation passed from parents to children. If a family member has been diagnosed with HNPCC, discuss your risk of the genetic syndrome with your doctor. If you've been diagnosed with HNPCC, ask your doctor what cancer screening tests you should undergo.