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We don't know exactly what causes womb cancer. But there are some things that we know may increase risk and others that seem to reduce risk. 

Risk factors for womb cancer

Womb cancer is strongly related to age. Most women diagnosed have had their menopause

Overweight or obese women are generally more likely to develop womb cancer than women of a normal weight.

Factors related to your menstrual history can increase the risk of womb cancer, including starting periods early and having a late menopause. 

Oestrogen only HRT (hormone replacement therapy) increases the risk of womb cancer. Women who take continuous combined HRT have a lower risk of womb cancer.

Having had a baby lowers your risk of womb cancer. If you have more than one child, you lower your risk even further. Most types of birth control pills also decrease your risk of womb cancer.

 

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How common womb cancer is

This section is about the most common type of womb cancer - endometrial cancer. The endometrium is the inner lining of the womb and all endometrial cancers start here. It is also called uterine cancer or cancer of the uterus. There is also information about rare types of womb cancer in this section.

Around 8,500 women are diagnosed with womb cancer in the UK each year. About 5 out of every 100 cancers diagnosed in women are womb cancers (5%). This makes it the 4th most common cancer in women in the UK.

 

What a risk factor is

A risk factor is anything that can increase your chance of developing cancer. 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 necessarily mean that you will not develop cancer. Some factors lower your risk of cancer and are known as protection factors.

We don't know exactly what causes endometrial cancer. Many of the risk factors relate to the body’s exposure to the female sex hormone, oestrogen. Or to the balance between oestrogen and another female sex hormone, progesterone. Oestrogen without progesterone to balance it increases the risk of womb cancer. Doctors call this unopposed oestrogen. The body stops making progesterone after the menopause, but still produces a small amount of oestrogen. So this explains why womb cancer is much more common in women after the menopause.

 

Age

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 (or HNPCC) are more likely to develop endometrial cancer at a younger age than the general population.

 

Being overweight

Women who are very overweight (obese) are generally 2 or 3 times as likely to develop womb cancer than women of a normal weight. Women who are very obese 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. Fat cells (also called adipose tissue) convert certain 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 studies show that higher levels of insulin are linked to an increased risk of womb cancer. This may be because the extra insulin can stimulate cancerous growth in the lining of the womb.

 

Diet and alcohol

Diet only seems to play a small role in womb cancer. If you eat a high fat diet you may have a higher risk of developing womb cancer. We don’t know whether this is directly to do with the fat in your diet, or because eating more fat tends to make you overweight. 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). Isoflavones are part of a group of plant chemicals known as phyto oestrogens. The way phyto oestrogens act is quite complex but they may block some of the effects of oestrogen. This seems to offer some protection from womb cancer. 

Coffee has been shown to reduce womb cancer risk, although we need more studies to be clear about this. Drinking tea may also decrease 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 research to be sure.

An analysis of studies has shown no link between drinking alcohol and the risk of womb cancer.

 

Having had children or not

If you have never been pregnant you are more likely to develop womb cancer than if you have 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 in pregnancy. Normally, at times during your menstrual cycle, there is oestrogen in your body without progesterone to balance it. Doctors call this unopposed oestrogen. Unopposed oestrogen increases the risk of womb cancer. Anything that stops this, even for a few months, lowers the risk of womb cancer.

 

Menstrual history

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
 

Thickened womb lining

Endometrial hyperplasia is a 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. Your doctor may advise a procedure called a D and C if you have these symptoms. D and C stands for dilation and curettage. It means opening up the cervix and scraping away the extra cells from inside the womb. The cells are then examined under a microscope to see if they are abnormal or not. Instead of a D and C your doctor may advise a hysteroscopy and a biopsy of the lining of the womb.

 

Polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a condition where cysts grow in the ovaries. Women with PCOS have a hormone imbalance which may cause very irregular periods. They are also more 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. But this may be because all the symptoms are also risk factors for womb cancer. A study showed that women under 55 who have PCOS have 4 times the risk of womb cancer than women of the same age who do not have PCOS.

Most women (more than 90%) who have  PCOS do not develop womb cancer.

 

Family history and other cancers

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.

Research has shown that daughters of women with womb cancer have double the risk of women in the general population.

Most cancers are not caused by a gene that you inherited. They are caused by gene changes in your lifetime as cells divide and grow to repair or replace old or damaged cells. Cancers due to these gene changes are called sporadic. But some cancers are caused by cancer genes that you were born with. 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 because of a faulty gene. But even if there is a faulty gene in your family, you may not have inherited it.

Hereditary non polyposis colon cancer (HNPCC) or Lynch syndrome is an inherited faulty gene associated with an increased risk of some cancers, especially bowel cancer. Other than bowel cancer, womb cancer is the most common cancer linked with this syndrome. Out of every 100 women who carry the HNPCC gene fault, 40 to 60 will develop womb cancer at some point in their lives. In this group of women, womb cancer tends to start at a younger age than in the general population. About 1 in 6 womb cancers in women with the HNPCC gene fault are diagnosed before the age of 40. 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.

 

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, you may be monitored for possible signs and symptoms of womb cancer. The major sign to look out for is unexpected bleeding. It is important to tell your doctor if your periods have stopped and you have any vaginal bleeding while you are taking tamoxifen.

If you have had breast cancer it is important to remember that the benefits of taking tamoxifen to prevent your breast cancer coming back are more important than the small risk of getting womb cancer.

 

Hormone replacement therapy (HRT)

Hormone replacement therapy is used by many women to control the symptoms of menopause. There are different types of HRT. Oestrogen only HRT increases the risk of womb cancer and is normally only prescribed to women who have had their womb removed (a hysterectomy). 

An analysis of studies has 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.

Women need to take into account the risk of other cancers when choosing whether to take HRT. Women taking combined HRT have a slightly increased risk of breast cancer. So if you are considering using HRT you need to discuss the risks and benefits of the treatment with your doctor.

We have more information about HRT and cancer risk.

 

Contraceptive pills

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.

 

Diabetes

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.

 

Physical activity

The World Cancer Research Fund has listed physical activity as being protective against womb cancer.

A Cancer Research UK study has shown that being inactive causes just under 4 out of 100 womb cancers (4%). In the study, moderate activity was described as taking at least 30 minutes of exercise 5 times a week. This needs to be exercise that makes you slightly short of breath. 

The link between physical activity and womb cancer may partly be because women who are more active generally have a lower bodyweight.

 

Aspirin

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.

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Updated: 22 October 2014