Risk factor and causes of womb cancer (endometrial cancer)
The exact cause of cancer of the womb isn’t known, but there are certain things that can increase a woman’s risk.
These are called risk factors. Having a risk factor doesn’t mean you will get cancer, just as not having a risk factor doesn’t mean that you won’t get it. The risk factors for womb cancer are mainly linked with how much of the hormone oestrogen the womb lining is exposed to.
Like most cancers, the risk of womb cancer increases with age.
A woman’s exposure to oestrogen and its balance with another hormone, called progesterone, affect the risk of womb cancer.
Before the menopause, the ovaries produce oestrogen and progesterone, which help to control the monthly cycle (periods). This includes releasing an egg from the ovaries and making the womb lining grow thicker to prepare for pregnancy.
When this doesn’t happen, the lining comes away as a period. After the menopause the ovaries no longer produce hormones, but women still produce some oestrogen in their body fat.
When there’s too much oestrogen without progesterone to balance it, the risk of womb cancer is increased.
Factors that influence this are:
Not having children
Women who haven’t had children, or who are unable to have children, have a greater risk of womb cancer. Oestrogen in the body is low during pregnancy, and the level of progesterone is high.
Menstrual history (periods)
Longer exposure to oestrogen can affect your risk of womb cancer. This can be
starting your periods early (before 12)
having a late menopause (after 55)
having longer periods
having irregular periods
not having periods.
Hormone replacement therapy (HRT)
Taking oestrogen-only HRT (which contains no progesterone) or a type of HRT called tibilone can increase the risk of womb cancer. Oestrogen-only HRT is usually only given to women who have had an operation to remove their womb (a hysterectomy).
Weight and physical activity
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Being overweight is an important risk factor for womb cancer. After the menopause, body fat is the main source of oestrogen. Women who are overweight may have a high level of oestrogen. One in three womb cancers may be caused by being overweight. There’s also some evidence that being less physically active can increase womb cancer risk.
Genetic factors (family history)
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A very small number of womb cancers may be caused by changes to a particular gene, which can increase the risk of developing it. Genes store the biological information we inherit from our parents. If there are several close relatives on the same side of the family with bowel, breast or womb cancer, there’s a possibility that there may be a genetic (inherited) link. Close relatives are parents, children, sisters and brothers.
If you’re worried about a family history of cancer, speak to your GP, who can reassure you or refer you to a family cancer clinic.
There are some known genetic (inherited) conditions that can increase the risk of womb cancer. Women with hereditary non-polyposis colorectal cancer (HNPCC) have a faulty gene that increases the risk of bowel cancer and also of womb cancer. Women who have this gene have a 30-60% risk of developing womb cancer over their lifetime. They are screened for bowel cancer and may also have tests to check for early signs of womb cancer.
We have more information about HNPCC.
Women with a rare genetic condition called Cowden syndrome have an increased risk of benign (non-cancerous) tumours and also of cancers, including womb cancer. But the increase in risk is small.
Tamoxifen is a hormonal drug used to treat breast cancer. It can slightly increase the risk of womb cancer, usually when it’s taken over a long period of time. But there are very clear benefits of taking tamoxifen that far outweigh this risk. Women taking tamoxifen always have tests done to check any unusual vaginal bleeding.
Other medical conditions
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Some other medical conditions may cause an increase in womb cancer risk. These include:
Thickening of the womb lining
(Endometrial hyperplasia) is a condition where the womb lining becomes thicker. Symptoms include heavy periods and bleeding between periods or after the menopause. When it’s diagnosed, women have treatment and/or regular tests.
Diabetes, which is linked with being overweight, increases a woman’s risk of womb cancer. There may also be a separate link between womb cancer and insulin, a hormone that regulates blood sugar.
Polycystic ovary syndrome (PCOS)
Women with PCOS, a condition in which cysts grow on the ovaries, may have fertility problems, infrequent or no periods, or may be very overweight or diabetic. These are all linked with womb cancer risk.
Uncommon ovarian cancers
Some types of ovarian cancers called granulosa and theca cell tumours can produce oestrogen, which increases the risk of womb cancer.
Many of the risk factors we’ve mentioned are not under our control, so we can’t do anything about them. But keeping to a healthy weight and being more physically active may help reduce a woman’s risk of womb cancer.
Women who take the combined contraceptive pill over a long period of time have a lower risk of womb cancer.