Endometrial cancer - Causes of womb cancer

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

Cancer begins with a change (mutation) in the structure of the DNA in cells, which can affect how they grow. This means cells grow and reproduce uncontrollably, producing a lump of tissue called a tumour.

If left untreated, cancer can grow and spread to other parts of your body, either directly or through the blood and lymphatic system.

Increased risk

A number of things have been identified that increase the risk of developing womb cancer. Some of these are discussed below.

Age

The risk of developing womb cancer increases with age. The majority of cases occur in women aged 40 to 74, with only 1% of cases being diagnosed in women under 40.

Oestrogen

The risk of developing womb cancer is linked to the body's exposure 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 between 25 and 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.

It's important to visit your GP if you're taking tamoxifen and experience any abnormal vaginal bleeding.

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 levels.

Many women with type 2 diabetes are also overweight, which further increases the risk.

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, which can cause symptoms such as irregular or light periods, or no periods at all, as well as 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 an increased risk of developing womb cancer.

Want to know more?

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