Causes of womb cancer

It is not known exactly what causes womb cancer, but certain things can increase your risk of developing it.

About cancer

The body is made up of millions of different cells. Cancer happens when some of the cells multiply in an abnormal way. When cancer affects organs and solid tissues, it causes a growth called a tumour to form. Cancer can occur in any part of the body where the cells multiply abnormally.

In most cases of womb cancer, the cells of the womb lining, called the endometrium, are usually affected. This is why womb cancer is sometimes called endometrial cancer.

Left untreated, cancer can quickly grow and spread from the womb into other tissues in the pelvis or to other parts of the body. This usually happens through the lymphatic system, but it can also spread through the bloodstream.

The lymphatic system is a series of glands that are located throughout the body and linked together in a similar way to the blood circulation system.

Once the cancer reaches your lymphatic system, it can spread to any other part of your body, including your bones, blood and organs.

Increased risk

Things that can increase your chances of developing womb cancer include:

Age

The risk of developing womb cancer increases with age, most cases develop in women who are over the age of 50.

Oestrogen

The risk of developing womb cancer is linked to the exposure of the body to oestrogen. Oestrogen is one of the hormones that regulates the reproductive system in women.

• Oestrogen stimulates the release of eggs from your ovaries and causes the cells of the womb lining to divide.
• Progesterone gets the lining of your uterus ready to receive the egg from the ovaries.

The levels of oestrogen and progesterone in your body are usually balanced with each other. If oestrogen isn’t kept in balance by progesterone, the level in the body can increase, this is called unopposed oestrogen.

After the menopause, the body stops producing progesterone. However, there are still small amounts of oestrogen being produced. This “unopposed oestrogen” causes the cells of the endometrium to divide, which can increase the risk of womb cancer.

Hormone replacement therapy (HRT)

Because of the link between increased levels of unopposed oestrogen and womb cancer, oestrogen-only hormone replacement therapy (HRT) should only be given to women who have had their womb surgically removed (hysterectomy).

In all other cases, both oestrogen and progesterone (combination HRT) must be used in HRT to reduce the risk of womb cancer.

Being overweight or obese

As oestrogen can be produced in fatty tissue, being overweight or obese increases the level of oestrogen in your body. This significantly increases your chances of developing womb cancer.

Women who are overweight are three times more likely to develop womb cancer compared with women who are a healthy weight. Very obese women are six times more likely to develop endometrial cancer compared with women who are a healthy weight.

One way to assess whether your weight is healthy is to calculate your body mass index (BMI). In the UK, people with a BMI of 25 to 30 are overweight, and those with an index above 30 are obese.

Reproductive history

Women who have not had children are at a higher risk of womb cancer. This may be because the increased levels of progesterone and decreased levels of oestrogen that occur during pregnancy have a protective effect on the lining of the womb.

Tamoxifen

Women who are treated with tamoxifen (a hormone treatment for breast cancer) can be at an increased risk of developing womb cancer. However, this risk is outweighed by the benefits that tamoxifen provides in preventing breast cancer.

Diabetes

Women with diabetes are twice as likely to develop womb cancer as women without the condition. Diabetes causes an increase in the amount of insulin in your body, which in turn can raise your oestrogen level.

Polycystic ovarian syndrome (PCOS)

Women with polycystic ovarian syndrome (PCOS) are at a higher risk of developing womb cancer, as they have high levels of oestrogen in their bodies. Women with PCOS have multiple cysts in the ovary, and this can cause symptoms such as irregular or light periods, or no periods at all, problems getting pregnant, weight gain, acne and excessive hair growth (hirsutism).

Endometrial hyperplasia

Endometrial hyperplasia is when the lining of the womb becomes thicker. Women with the condition may be at increased risk of developing womb cancer.

Want to know more?

• Cancer Research UK: womb cancer risks and causes
• Macmillan: causes of womb cancer