What are the risk factors for endometrial cancer?

We do not yet know what causes most cases of endometrial cancer. But we do know that certain risk factors are linked to this disease. A risk factor is anything that changes a person's chance of getting a disease such as cancer. Different cancers have different risk factors. For example, being in strong sunlight without protection is a risk factor for skin cancer. Smoking is a risk factor for many cancers. Some risk factors, like your age or race, can't be changed. Others, like smoking and diet are under your control.

But risk factors don't tell us everything. Someone can have several risk factors and still not get a disease. Also, not having any risk factors doesn't mean that you won't get the disease. Even if a woman with endometrial cancer has one or more risk factors, there is no way to know which, if any, of these factors played a part in her cancer.

Risk factors for endometrial cancer

Hormone factors

A woman's hormone balance plays a part in most endometrial cancers. Many of the risk factors for endometrial cancer affect estrogen levels. Before change of life, the ovaries are the main source of the 2 main types of female hormones -- estrogen and progesterone. The balance between these hormones changes during a woman's menstrual cycle each month. A shift in the balance of these 2 hormones toward more estrogen increases a woman's risk for getting endometrial cancer.

After change of life, the ovaries stop making these hormones, but a small amount of estrogen is still made in fat tissue. Female hormones can also be taken as birth control pills to prevent pregnancy and as hormone therapy to treat symptoms of menopause.

Estrogen therapy: Using estrogen to treat symptoms of change of life is known as estrogen therapy or menopausal hormone therapy. Estrogen treatment can reduce hot flashes, improve vaginal dryness, and help prevent the weakening of the bones (osteoporosis) that can happen with menopause. But the use of estrogen by itself increases a woman's risk of getting endometrial cancer in women who still have a uterus. Estrogen therapy also increases a woman's chance of developing serious blood clots and heart disease.

Studies show that giving progesterone-type drugs along with the estrogens helps lower the risk of endometrial cancer. But studies also show that giving this combination of the hormones increases a woman's chance of getting breast cancer and blood clots.

It is important to discuss the pros and cons of estrogen therapy with your doctor. If you choose to take it, you should use the lowest dose that is needed for the shortest period of time. You should also have follow-up pelvic exams at least every year. Let your doctor know right away if you have any vaginal bleeding or discharge that isn't normal.

Birth control pills: Using birth control pills lowers the risk of endometrial cancer. The risk is lowest in women who take the pill for a long time. And this protection goes on for at least 10 years after a woman stops taking this form of birth control. But you need to look at all of the pros and cons when choosing a birth control method -- endometrial cancer risk is only one factor to think about. It's a good idea to talk to your doctor about the different methods of birth control to find the one that is best for you.

Total number of menstrual cycles (periods): Having more periods during a woman's lifetime raises her risk of endometrial cancer. Starting periods before age 12 or going through change of life late raises the risk. Starting periods early is less a risk factor for women with early change of life. Likewise, late change of life may not lead to a higher risk in women whose periods began later in their teens.

Pregnancy: During pregnancy, the hormone balance shifts toward more progesterone. So having many pregnancies reduces endometrial cancer risk. Women who have never been pregnant have a higher risk.

Obesity (being very overweight): Most of a woman's estrogen is made by her ovaries, but fat tissue can change some other hormones into estrogens. Having more fat tissue can increase a woman's estrogen levels and, as a result, increase her endometrial cancer risk.

Tamoxifen: Tamoxifen is a drug that is used to treat women with breast cancer. It is also used to reduce the risk in women who are at a high risk of getting breast cancer. The drug acts like estrogen in the uterus. It can cause the uterine lining to grow and increase the risk of endometrial cancer.

The risk of getting endometrial cancer in women taking tamoxifen is fairly small (about 1 in 500). It must be balanced against the value of this drug in treating and preventing breast cancer. This is something women may want to talk about with their doctors. If you decide to take tamoxifen, you should have yearly pelvic exams. You should also be sure to tell your doctor if you have any endometrial cancer symptoms, such as discharge or bleeding that isn't normal.

Ovarian tumors: A certain type of ovarian tumor makes estrogen. Women who have these tumors have higher than normal estrogen levels. The increase in estrogen compared to progesterone can increase a woman's chance of getting endometrial cancer.

Polycystic ovarian syndrome: Women with polycystic ovarian syndrome (PCOS) have hormone levels that are not normal, such as higher androgen (male hormones) and estrogen levels and lower levels of progesterone. The increase in estrogen compared to progesterone can increase a woman's chance of getting endometrial cancer.

Use of an IUD (intrauterine device)

Women who used an IUD for birth control seem to have a lower risk of getting endometrial cancer. This only applies to IUDs that do not contain hormones. Researchers have not yet studied whether newer types of IUDs that release hormones have any effect on endometrial cancer risk.

Age

The risk of endometrial cancer goes up as a woman gets older.

Diet and exercise

A high-fat diet can increase the risk of many cancers, including endometrial cancer. Because fatty foods are also high-calorie foods, a high-fat diet can lead to obesity, which is also an endometrial cancer risk factor. Some doctors think that fatty foods may have a direct effect on estrogen levels, which can increase risk, too.

Exercise protects against endometrial cancer. Studies found that women who exercised more had a lower risk of this cancer, while one study showed that women who spent more time sitting had a higher risk.

Diabetes

Diabetes is more common in people who are overweight. This could be why diabetes is a risk factor for endometrial cancer. But some studies suggest that diabetes by itself, even when the person is not overweight, could be a risk factor.

Family history

Endometrial cancer appears to run in some families who also tend to get colon cancer. This is called HNPCC (hereditary nonpolyposis colon cancer), also known as Lynch syndrome. This results in a very high risk of colon cancer, as well as a high risk of endometrial cancer. There are some families that have a high rate of only endometrial cancer. These families may have a different genetic disorder that hasn't been discovered yet.

Breast or ovarian cancer

Women who have had breast cancer or ovarian cancer may have a higher risk of getting endometrial cancer. Some of the risk factors for breast and ovarian cancer also increase endometrial cancer risk.

Earlier pelvic radiation therapy

Radiation used to treat some other cancers can damage the DNA of cells. This could increase the risk of getting a second type of cancer, such as endometrial cancer.

Endometrial hyperplasia

Endometrial hyperplasia is an increased growth of the endometrium. The most common type has a very small risk of becoming cancer. It may go away on its own or after treatment with hormones. If the hyperplasia is called “atypical,” it has a higher chance of becoming a cancer.

It is important to keep in mind that although these factors may increase a woman's risk for getting endometrial cancer, they do not always cause the disease. Many women with one or more of these risk factors never get endometrial cancer, and some women with endometrial cancer do not have any of these risk factors.