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.
The risk of womb cancer increases with age. Most women diagnosed with womb cancer have had their menopause. And 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.
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 womens reproductive cycle.
After the menopause the ovary stops 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 divide increasing the risk of mistakes being made. So anything that increases the amount of oestrogen in your body increases your risk of womb cancer.
Being overweight or obese is the biggest preventable risk factor of womb cancer. Women who are very overweight (obese) are 2.5 times more likely to develeop womb cancer than women of a healthy weight.
A Cancer Research UK study published in 2011 found that being overweight or obese causes around a third of womb cancers in the UK each year.
Higher levels of oestrogen
Overweight women have higher levels of oestrogen. Fat cells covert hormones into a type of oestrogen. So the more body fat you have, generally the more oestrogen you produce. When more oestrogen is produced, 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.
Insulin helps the body to unlock and use the energy in food that we eat. People who are overweight can sometimes become resistant to insulin. This means that although the body produces insulin, the insulin doesn’t work as well as usual. To make up for this, the body makes too much.
Some research has shown higher levels of insulin are linked to an increased risk of womb cancer. The extra insulin tells cells to divide more quickly in the womb lining, increasing the chance of cancer cells being produced.
Diet and alcohol
Studies have looked at whether diet could affect womb cancer risk. At the moment there are no convincing dietary factors that directly increase or decrease your womb cancer risk. But a healthy diet helps you keep a healthy weight, which in turn reduces the risk of womb cancer.
Coffee has also been linked to a reduced womb cancer risk. But overall the evidence is not strong.
An analysis of studies hasn't shown a link between drinking alcohol and the risk of womb cancer. But alcohol increases the risk of many other types of cancer.
Having had children
Studies show having children lowers womb cancer risk by around a third. The risk decreases with the more children a women has.
Oestrogen levels are low and 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.
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. You have a higher risk of developing womb cancer if you have this thickening, 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. 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 and type 2 diabetes. These are 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 gene fault, 40 to 60 will develop womb cancer at some point in their lives.
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.
Tamoxifen is a hormone therapy for some types of breast cancer. It can increase womb cancer risk, as it is thought to have a similar effect to oestrogen on the womb. This is a rare side effect of taking it.
And 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
Hormone replacement therapy (HRT)
There are different types of hormone replacement therapy (HRT). Oestrogen only HRT increases the risk of womb cancer. Because of this, doctors normally only prescribe oestrogen only HRT for women who have had their womb removed (a hysterectomy).
Combined HRT contains the hormones oestrogen and progesterone. There is evidence that the progesterone part can counteract the cancer causing effects of the oestrogen part. But it depens on the type of combined HRT used.
The contraceptive pill
The combined pill, the most common type of birth control pill, is linked with a reduced risk of womb cancer. These protective effects are bigger the longer a woman takes the combined pill for. 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.
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 and we need more research to find out about why it increases risk.
The world cancer research fund has listed physical activity as probably being protective against womb cancer.
This link may partly be because women who are more active have a lower body weight. Being physically active also helps to control hormones in the body, such as oestrogen and insulin.
Aspirin may reduce the risk of womb cancer in women who are very overweight (obese). But more studies are needed to confirm this link.
At the moment there are no recommendations to take aspirin to reduce womb cancer risk.
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.