The cause of breast cancer is unknown. However, it is most unlikely that there is one single cause. A number of factors, some known and many unknown, probably work together to trigger its growth. Breast cancer usually occurs in women over 50 and all women are at risk as they grow older. Although breast cancer does occur in women under 50, increasing age is the main factor influencing the risk of getting breast cancer. The factors listed below also seem to put women at slightly higher risk. However, they explain only a small number of breast cancer cases.
Women with a strong family history of breast cancer have an increased chance of getting breast cancer and a 60% increased risk of ovarian cancer. The increase in risk can be very small to quite large (only 5-10% of all breast cancers are hereditary), depending upon the number of relatives affected, the age of the relatives when their breast cancer was found, and the type of breast cancer they had.
Researchers are looking into a number of factors which may influence the development of breast cancer. Because breast cancer is more common in certain countries, lifestyle factors, such as diet are thought to be important. (Did you know that two glasses of wine each day could give you an increased risk of 41%?). Women who have already had breast cancer do have a slightly higher chance of a new breast cancer developing in their other breast.
Hormone changes linked with pregnancy and menopause also appear to have an effect. None of these factors are certain enough though, to predict who will develop breast cancer. Risks linked with the pill suggest a possible increased risk of 10% and women on HRT can have an increased risk of up to 35%.