Womb cancer is the 4th most common cancer in women in the UK. We don't know what causes most womb cancers. But there are some factors that can increase your risk of developing it.
What a risk factor is
Anything that increases your risk of getting a disease is called a risk factor. Different cancers have different risk factors.
Having a risk factor does not necessarily mean that you will develop cancer. Also, not having any risk factors does not mean that you definitely won't get cancer.
Some factors lower your risk of cancer and are known as protection factors.
Most women diagnosed with womb cancer have had their menopause. Almost three quarters of cases of womb cancer are in women aged 40 to 74.
Just over 1 in 100 cases (1%) are diagnosed in women under 40. Women who have a particular gene fault called Lynch syndrome are more likely to develop endometrial cancer at a younger age than the general population.
Lynch syndrome used to be called hereditary nonpolyposis colorectal cancer (HNPCC). About 3 out of every 100 cases (3%) of endometrial cancers are linked to Lynch syndrome.
Very overweight (obese) women are generally 2 or 3 times as likely to develop womb cancer than women of a healthy weight. Very obese women may increase their risk by up to 6 times.
A Cancer Research UK study published in 2011 found that being overweight or obese causes around a third of womb cancers. This is probably because overweight women have higher levels of oestrogen. When more oestrogen is made, the lining of the womb builds up. When more lining (endometrial) cells are produced, there is a greater chance of one of them becoming cancerous.
Another reason for the higher risk of womb cancer in overweight women may be related to insulin. People who are overweight can sometimes become resistant to insulin. This means that although the body produces insulin, it doesn’t work as well as usual. To make up for this, the body makes too much. Some studies show that higher levels of insulin are linked to an increased risk of womb cancer. The extra insulin may stimulate cancerous growth in the lining of the womb.
Diet and alcohol
The World Cancer Research Fund lists red meat as a possible cause of endometrial cancer.
Some studies have reported a lower risk of womb cancer in women who eat a lot of isoflavones (found in soya based foods). Coffee and tea may also reduce womb cancer risk. Green tea has a stronger effect than black tea.
There is some evidence that a higher intake of vegetables reduces womb cancer risk. But we need more studies to be sure.
An analysis of studies has shown no link between drinking alcohol and the risk of womb cancer.
Having had children
Studies show that having children lowers your risk by more than a third. The risk decreases with the more children you have.
Oestrogen levels are low and progesterone levels are high during pregnancy. Normally during your menstrual cycle, there is oestrogen in your body without progesterone. Doctors call this unopposed oestrogen. Unopposed oestrogen increases the risk of womb cancer. Anything that stops this, such as pregnancy,lowers the risk of womb cancer.
Menstrual historySome factors linked with periods (menstruation) can increase your risk of womb cancer because they cause higher levels of oestrogen. These include:
- starting your period at a young age
- a late menopause
Thickened womb lining
Endometrial hyperplasia is a non cancerous (benign) condition where the lining of the womb becomes thicker. If you have this thickening you have a higher risk of developing womb cancer, especially if the extra lining cells are abnormal. Symptoms of endometrial hyperplasia are heavy periods, bleeding between periods, and bleeding after menopause.
Polycystic ovary syndrome
Women with polycystic ovary syndrome (PCOS) have a hormone imbalance which may cause very irregular periods. They are also likely to be insulin resistant, overweight and have diabetes. They have an increased risk of womb cancer compared to women who don’t have PCOS. This may be because all the symptoms are also risk factors for womb cancer.
Research has shown that daughters of women with womb cancer have double the risk of women in the general population.
If you have several close relatives on the same side of the family who have had bowel cancer or womb cancer you may be at increased risk of womb cancer.
Lynch syndrome is an inherited faulty gene linked with an increased risk of some cancers, including bowel cancer and womb cancer. Out of every 100 women who carry this rare gene fault, 40 to 60 will develop womb cancer at some point in their lives. But it is important to remember that womb cancers in these women are often picked up at an early stage and so are more likely to be cured.
You are at a slightly increased risk of getting womb cancer if you have had breast or ovarian cancer in the past. This may be because of shared lifestyle or environmental factors. For example, the risk of womb cancer in breast cancer survivors is higher in those who are overweight. The increase in risk of womb cancer may also be due to treatment for cancer, such as tamoxifen.
An increased risk of womb cancer is a known side effect of taking tamoxifen, which is a hormonal therapy for breast cancer. Scientists think this is because the drug has a similar effect on the womb to oestrogen.
If you have been taking tamoxifen for more than 2 years or so, your doctor will monitor you for possible signs and symptoms of womb cancer. The main sign to look out for is unexpected vaginal bleeding. It is important to tell your doctor if your periods have stopped and you have any bleeding while you are taking tamoxifen.
Hormone replacement therapy (HRT)
There are different types of HRT. Oestrogen only HRT increases the risk of womb cancer. Doctors normally only prescribe this to women who have had their womb removed (a hysterectomy).
Studies have shown a decreased risk of womb cancer in women who have taken continuous combined HRT (containing oestrogen and progesterone) compared to women who have never had HRT.
Most types of birth control pills used today decrease the risk of womb cancer. These contain either a combination of oestrogen and progesterone (combination pills), or progesterone only (mini pills). This link may be limited to women who have taken the pill for 5 years or more. The protective effect is thought to last as long as 20 years after stopping taking it.
Using a non hormonal intrauterine device (IUD or coil) may also decrease the risk of womb cancer.
Several studies show a higher risk of womb cancer in women with diabetes. This link is not thought to be due to being overweight, or because of the treatment for diabetes.
The World Cancer Research Fund has listed physical activity as being protective against womb cancer. This link may partly be because women who are more active generally have a lower bodyweight.
A Cancer Research UK study has shown that being inactive causes just under 4 out of 100 womb cancers (4%).
Aspirin may protect against womb cancer, particularly in women who are very overweight. But more studies are needed.
It is important to remember that doctors don't recommend taking aspirin regularly due to its side effects. This drug can damage the lining of your stomach and cause bleeding.
Other possible causes
Stories about potential causes of cancer are often in the media and 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.