Risks and causes of womb cancer

Being overweight or obese is one of the biggest risks of womb cancer in the UK. There are some other risk factors that can increase your risk of developing womb cancer.

Womb cancer is also called uterine cancer. This is because the uterus is the medical name for the womb. You may also hear it called endometrial cancer. The endometrium is the lining of the womb. 

What is a risk factor?

Anything that can increase your risk of getting a disease is called a risk factor.

Different cancers have different risk factors.­ Having one or more of these risk factors doesn't mean you will definitely get that cancer.

Age

The risk of womb cancer increases with age. Most women diagnosed with womb cancer have been through their menopause and are aged 75 to 79.

Being overweight

Being overweight or obese is the biggest preventable risk factor for womb cancer. Being overweight or obese causes around a third of womb cancers. 

Higher levels of oestrogen

Women who are obese or overweight have higher levels of oestrogen than those who are not. Fatty tissues produce more oestrogen. So the more body fat you have, generally the more oestrogen you produce. The more oestrogen you make, the more the womb's lining builds up.

When more lining cells are produced, there is a greater chance of one of them becoming cancerous.

Oestrogen

Oestrogen is a female hormone. Before the menopause, the ovaries make most of the oestrogen a woman needs. Along with another female hormone called progesterone, it regulates women's reproductive cycle. 

After menopause, the ovaries stop producing hormones. But the body continues to make a small amount of oestrogen. Fat cells also make oestrogen. 

Oestrogen causes the cells in the womb to grow and divide. Cancer happens when there is a mistake when the cells are growing and dividing. So, if there are more cells, it increases the risk of mistakes happening. Anything that increases the amount of oestrogen in your body increases your risk of womb cancer.

Hormone replacement therapy (HRT)

There are different types of hormone replacement therapy (HRT). Oestrogen only HRT increases the risk of womb cancer. This is why doctors usually prescribe oestrogen only HRT for women who have had surgery to remove their womb (a hysterectomy).

Combined HRT contains the hormones oestrogen and progesterone. Progesterone counteracts the effects of the oestrogen. But it depends on the type of combined HRT you take. 

HRT is an effective treatment for symptoms of menopause. For most people, the benefits of taking HRT outweigh the risks.

Your doctor can prescribe HRT and help you make an informed choice about what is right for you.

Tamoxifen

Tamoxifen is a hormone therapy for some types of breast cancer. It can increase womb cancer risk. It appears to have a similar effect to oestrogen on the womb. This is a rare side effect of taking it.

The benefits of taking tamoxifen as part of your treatment for breast cancer outweigh the small risk of womb cancer.

If you are taking tamoxifen, tell your doctor if you have:

• unexpected vaginal bleeding
• vaginal bleeding after your periods have stopped 

Diabetes

Several studies show a higher risk of womb cancer in women with diabetes for both Type 1 and Type 2. This link may be due to being overweight. We need more research to find out why it increases risk.

Thickened womb lining

Endometrial hyperplasia is a non cancerous (benign) condition where the womb's lining becomes thicker. You have a higher risk of developing womb cancer if you have atypical hyperplasia.

Symptoms of endometrial hyperplasia are:

• heavy periods
• bleeding between periods
• bleeding after menopause.

Polycystic ovary syndrome

Women with polycystic ovary syndrome (PCOS) have a hormone imbalance which may cause very irregular periods. Women with PCOS have an increased risk of womb cancer compared to women who don't have PCOS. The cause of the increase is unclear but it may be due to the hormone imbalance.  

Polycystic ovary syndrome is also linked with:

• insulin resistance
• being overweight
• type 2 diabetes

These are risk factors for womb cancer. 

Menstrual history

Some factors linked with periods (menstruation) can increase your risk of womb cancer. This is because they cause higher levels of oestrogen. These include: 

• starting your period at a young age

• a late menopause

Family history

A family history of womb cancer is associated with an increased risk of endometrial cancer. This may be due to genetic factors, but research is ongoing to understand this better.

Lynch syndrome

If you have a family history of Lynch syndrome, you may also be at increased risk of womb cancer.

Lynch syndrome is an inherited faulty gene. It is linked with an increased risk of several cancers, including womb cancer. Out of every 100 women who carry this gene fault, up to 49 will develop womb cancer at some point in their lives.

Having had children decreases your risk

Studies show having children lowers womb cancer risk. The risk decreases with the number of children a woman has. 

Oestrogen levels are low, while progesterone levels are high during pregnancy. During the menstrual cycle, there is oestrogen in the body without progesterone. This is called unopposed oestrogen. 

Unopposed oestrogen increases womb cancer risk. So anything that stops this (such as pregnancy) lowers the risk of womb cancer. 

The contraceptive pill is linked to a reduced risk

The combined pill, the most common type of birth control pill, is linked with a reduced risk of womb cancer. The protective effects are more the longer a woman takes the combined pill. They can continue for decades after she stops taking it. 

Using a non hormonal intrauterine device (IUD or coil) has also been linked with a decreased risk of womb cancer.

Physical activity and coffee might reduce the risk

Physical activity

Physical activity is thought to probably be protective against womb cancer. 

This link may partly be because more active women have a lower body weight. Being physically active also helps to control hormones in the body, such as oestrogen and insulin. 

Drinking coffee

Some studies show coffee as probably protective against womb cancer, but we need more research to understand this.

Coffee contains caffeine that affects some people more than others. So, drinking large amounts can interfere with sleep. Adding a lot of sugar and cream to coffee can increase the risk of weight gain.

More information on risk factors for womb cancer

Other possible causes

There are often stories about potential causes in the media. It isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.

Reducing your risk

There are ways you can reduce your risk of cancer.