Uterine cancer (also called womb cancer) affects about 1 in 75 women. It usually occurs in those over the age of 50 with only 1 in 20 of all womb cancers occurring in women younger than 40.
As with most other cancers, the exact cause of uterine cancers is not known, but there are some things that are known to make a woman more likely to develop uterine cancer. The correct balance of the two main female hormones, oestrogen and progesterone, are important in the development of uterine cancer. So, either an excess of the hormone oestrogen (which stimulates the uterine lining), or a lack of progesterone (which seems to have a protective effect) are thought to increase the likelihood of uterine cancer.
The strongest risk factor of all is taking 'oestrogen only' hormone replacement therapy (HRT) - this can increase the risk of uterine cancer up to 15 times. However, when this was discovered in the 1970s giving this sort of HRT to women who still had their uterus (womb) was stopped. Nowadays women who have a uterus are given combination HRT.
Another risk factor is being overweight or obese. The reason for this is that the fat in women's bodies converts natural testosterone-like hormones to oestrogen-like hormones, and the more fat there is available for this, then the more oestrogens there are around.
Some of the other risk factors for uterine cancer are unfortunately difficult to avoid or control. These include some types of infertility, a late menopause, heavy bleeding at menopause, and medical conditions such as diabetes and high blood pressure.
Most uterine cancers do not run in families, however some of the risk factors listed above are genetically passed on, so risk for uterine cancer can be inherited 'indirectly'.
Having children or taking the oral contraceptive pill are two things which seem to substantially decrease the risk of uterine cancer - this seems to be related to the higher levels of the protective progesterone hormones which occur during pregnancy and which are present in the birth control pill.