A risk factor is any factor that is associated with increasing someone’s chances of developing a certain condition, such as cancer. Some risk factors are modifiable, such as lifestyle or environmental risk factors, and others cannot be modified, such as family history and inherited factors.
Having 1 or more risk factors does not mean that a person will develop cancer. Many people have at least 1 risk factor but will never develop cancer, while others with cancer may have had no known risk factors. Even if a person with cancer has a risk factor, it is usually hard to know how much that risk factor contributed to the development of their disease.
Risk factors for endometrial cancer include:
- obesity (often with diabetes and high blood pressure)
- history of chronic anovulation, including polycystic ovary syndrome (PCOS)
- treatment with oestrogen that is not given along with progesterone therapy
- treatment with tamoxifen
- family history of endometrial, ovarian or colon cancer, or Lynch syndrome
- never being pregnant.
Endometrial cancer is not infectious. It is not caused by sexual activity and cannot be passed on through sex.
The body makes some of its oestrogen in fatty tissue. Because of this, obese women are more likely than women in the normal weight range to have higher levels of oestrogen in their bodies. High levels of oestrogen may be the reason that obese women have an increased risk of developing endometrial cancer.
The risk of endometrial cancer is also higher in women with diabetes or high blood pressure, which occur in many obese women.
Anovulation is when an egg is not released from the ovary during the menstrual cycle. If this happens over many cycles, it is called chronic anovulation. This can increase the risk of developing endometrial cancer.
PCOS can cause chronic anovulation, and this syndrome is therefore a risk factor for endometrial cancer.
Hormone replacement therapy (HRT) is used to control the symptoms of menopause. Women who use HRT that contains oestrogen without progesterone (known as ‘unopposed oestrogen’) have an increased risk of developing endometrial cancer. Long-term use and large doses of unopposed oestrogen seem to increase this risk.
Progesterone protects the uterus, so women who use a combination of oestrogen and progesterone have a lower risk of endometrial cancer than women who use oestrogen alone.
There is no evidence of sufficient quality about the safety and effectiveness of natural or bio-identical hormones. Bio-identical hormones come in the form of lozenges, troches or creams. Many of these preparations contain unopposed oestrogen and are likely to carry the same risks as other types of HRT.
You should discuss the benefits and risks of HRT, including unopposed oestrogen use, with your doctor. Regular check-ups while taking unopposed oestrogen may improve the chance that the doctor will find endometrial cancer at an early stage, if it does develop. Always tell your doctor if you have any irregular bleeding.
Women who take the medicine tamoxifen to prevent or treat breast cancer have an increased risk of developing endometrial cancer. This risk appears to be related to the oestrogen-like effect of tamoxifen on the uterus. Women who take tamoxifen, or are considering taking tamoxifen, should discuss their personal and family medical history with their doctor.
Women who take tamoxifen should see their doctor immediately if they are postmenopausal and have vaginal bleeding, or if they are premenopausal and have bleeding between menstrual periods or a significant change in the nature of their periods.
In a small number of women, endometrial cancer may be caused by a faulty gene in a condition known as Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer, or HNPCC). Lynch syndrome increases the risk of endometrial, ovarian, bowel and some other cancers, and these cancers often occur at a younger age than in people who don’t have Lynch syndrome.
Lynch syndrome is caused by a fault in 1 of the ‘mismatch repair’ genes that normally help to protect a person from getting cancer. However, not everyone with the gene fault will develop cancer.
If your family is affected by Lynch syndrome, you should talk to your doctor about the current recommendations for prevention and screening for bowel cancer, and to be referred to a family cancer clinic.
Your doctor can also help you find out if your family history is of concern. If necessary, the doctor may refer you to a family cancer clinic for genetic counselling, information and support.
Pregnancy shifts the hormonal balance towards progesterone, which can protect the uterus. Having many pregnancies can protect against endometrial cancer. Women who have never been pregnant have a higher risk of endometrial cancer, especially if they are also infertile (unable to become pregnant).
Factors that reduce risk
The following factors may decrease your risk of developing endometrial cancer:
- keeping your body weight in the normal range
- taking oral contraceptives (birth control pills, or ‘the pill’) that combine oestrogen and progestin
- physical activity
- being pregnant or breastfeeding.
Find out more:
- Lifestyle and risk reduction
- Position Statement on Lifestyle risk factors and the primary prevention of cancer