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Risk factors
By Mayo Clinic staff
The female reproductive system consists of two ovaries, two fallopian tubes, a uterus and a vagina. The ovaries produce two main female hormones — estrogen and progesterone. The balance between these two hormones changes each month, making the endometrium thicken during the early part of the monthly cycle. If no pregnancy occurs, the endometrium is then shed during the last phase of the menstrual cycle.
When the balance of these two hormones shifts toward more estrogen — which stimulates growth of the endometrium — a woman's risk of developing endometrial cancer increases. Factors that increase levels of estrogen in the body include:
- Many years of menstruation. If you started menstruating at an early age — before age 12 — or you began menopause later, you're at greater risk of endometrial cancer than is a woman who menstruated for fewer years. The more years you have had periods, the more exposure your endometrium has had to estrogen.
- Never having been pregnant. Pregnancy seems to decrease the risk of endometrial cancer, although experts aren't sure exactly why this might be. The body produces more estrogen during pregnancy, but it produces more progesterone, too. Increased progesterone production may offset the effects of the rise in estrogen levels. It's also possible that not having been pregnant may be the result of infertility caused by irregular ovulation, which may be the reason why women who've never been pregnant are at an increased risk of endometrial cancer.
- Irregular ovulation. Ovulation, the monthly release of an egg from an ovary in menstruating women, is regulated by estrogen. Irregular ovulation or failure to ovulate increases your lifetime exposure to estrogen. Ovulation irregularities have many causes, including obesity and a condition known as polycystic ovary syndrome (PCOS). This is a condition in which hormonal imbalances prevent ovulation and menstruation. Treating obesity and managing the symptoms of PCOS can help restore your monthly ovulation and menstruation cycle, decreasing your risk of endometrial cancer.
- Obesity. Ovaries aren't the only source of estrogen. Fat tissue can produce estrogen. Being obese can increase the level of estrogen in your body, putting you at a higher risk of endometrial cancer and other cancers. Obese women have three times the risk of endometrial cancer and overweight women have twice the risk, according to the American Cancer Society. However, thin women can also develop endometrial cancer.
- A high-fat diet. This type of diet may add to your risk of endometrial cancer by promoting obesity. Or, fatty foods may directly affect estrogen metabolism, further increasing a woman's risk of endometrial cancer.
- Diabetes. Endometrial cancer is more common in women with diabetes, possibly because obesity and type 2 diabetes often go hand in hand. However, even women with diabetes who aren't overweight have a greater risk of endometrial cancer.
- Estrogen-only replacement therapy (ERT). Estrogen stimulates growth of the endometrium. Replacing estrogen alone after menopause may increase your risk of endometrial cancer. Taking synthetic progestin, a form of the hormone progesterone, with estrogen — combination hormone replacement therapy — causes the lining of the uterus to shed and actually lowers your risk of endometrial cancer. However, this combination may cause other health risks, such as blood clots or breast cancer.
- Ovarian tumors. Some tumors of the ovaries may themselves be a source of estrogen, increasing estrogen levels.
Other factors that can increase your risk of endometrial cancer include:
- Age. The older you are, the greater your risk of endometrial cancer. The majority of endometrial cancer occurs in women older than 55.
- Personal history of breast cancer or ovarian cancer. If you've had breast or ovarian cancer, you may have an increased risk of endometrial cancer because all of these cancers share some of the same risk factors. However, the vast majority of women who have either breast or ovarian cancer never develop endometrial cancer.
- Tamoxifen treatment. One in every 500 women whose breast cancer was treated with tamoxifen will develop endometrial cancer. Although tamoxifen acts mostly as an estrogen blocker, it does have some estrogen-like effects and can cause the uterine lining to grow. If you're being treated with this hormone, see your doctor for an annual pelvic examination and be sure to report any unusual vaginal bleeding.
- Race. Black women have an increased risk of death from endometrial cancer, although white women are more likely to develop endometrial cancer.
- Hereditary nonpolyposis colorectal cancer (HNPCC). This inherited disease is caused by an abnormality in a gene important for DNA repair. Women with HNPCC have a significantly higher risk of endometrial cancer as well as colon and other cancers. The risk of endometrial cancer over a lifetime for women who have HNPCC mutations is between 40 and 60 percent, according to the American Cancer Society.
Having risk factors for endometrial cancer doesn't mean you'll get the disease. It means that you're at risk and should be alert to possible signs and symptoms of the disease. Conversely, some women who develop endometrial cancer appear to have no risk factors for the disease.
- Detailed guide: Endometrial cancer. American Cancer Society. http://documents.cancer.org/140.00/140.00.pdf. Accessed Sept. 9, 2008.
- Endometrial cancer treatment (PDQ). National Cancer Institute. http://www.cancer.gov/cancertopics/pdq/treatment/endometrial/patient/allpages/print. Accessed Sept. 16, 2008.
- Bakkum-Gamez JN, et al. Current issues in the management of endometrial cancer. Mayo Clinic Proceedings. 2008;83(1):97-112.
- Sorosky JI. Endometrial cancer. Obstetrics and Gynecology. 2008;111(2, Part 1):436-447.
- Moynihan T (expert opinion). Mayo Clinic, Rochester, Minn. Sept. 21, 2008.
