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 is a risk factor?
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 protective factors.
The risk of womb cancer increases with age. Most women diagnosed with womb cancer have been through their menopause. And almost three quarters of cases of womb cancer are in women aged 40 to 74.
Being overweight or obese is the biggest preventable risk factor of 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. Fat cells convert hormones into a type of oestrogen. So the more body fat you have, generally the more oestrogen you produce. The more oestrogen you produce the more the lining builds up.
When more lining cells are produced, there is a greater chance of one of them becoming cancerous.
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 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 being 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 normally only prescribe oestrogen only HRT for women who have had surgery to remove their womb (a hysterectomy).
Combined HRT contains the hormones oestrogen and progesterone. There is evidence that the progesterone can counteract the effects of the oestrogen. But it depends on the type of combined HRT you take.
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
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 why it increases risk.
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
- 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.
Some 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
Research has shown that daughters of women with womb cancer have double the risk of developing it compared to 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.
Having had children decreases your risk
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.
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 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.
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.
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.
Physical activity is thought to probably be 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.
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.