About 44,100 people in the UK each year are diagnosed with breast cancer. The causes of breast cancer are not yet completely understood. The risk of developing breast cancer is very small in young women and increases as women get older. More than half of breast cancers occur in women over the age of 65.

Some factors may slightly increase a woman’s risk of developing the disease and these are described below.

• Having had breast cancer.
• Having had certain types of benign breast disease (lobular carcinoma in situ or atypical lobular hyperplasia).
• Women who are taking hormone replacement therapy (HRT), or have recently taken it, have a slightly increased risk of breast cancer. Detailed information about HRT and breast cancer is in our health professionals section. Younger women who take HRT because they have had an early menopause, or have had their ovaries removed, do not have an increased risk of breast cancer until after the age of 50.
• Taking the contraceptive pill very slightly increases a woman's chance of developing breast cancer.
• Women who do not have children are slightly more likely to develop breast cancer then women who have children.
• Women who start their periods early (early puberty) or have a late menopause have a slightly higher risk of breast cancer.
• Women who have never breastfed are slightly more likely to develop breast cancer than women who have breastfed for more than a year.
• Being overweight, once you have had your menopause, can increase the risk of breast cancer.
• Drinking a lot of alcohol over many years can increase the risk.

Inherited faulty genes

A very small number (from 1 in 20 to 1 in 10) of breast cancers are thought to be caused by inherited faulty genes. Two breast cancer genes have been identified: BRCA1 and BRCA2 – others may be found in the near future.

Breast cancer is a common cancer and about one in nine women in the UK will develop it during their lifetime. So, in a family if just one or even two elderly relatives are diagnosed with breast cancer, it is not likely that the cancers could be caused by an inherited faulty gene. Other family members would not be at high risk of developing breast cancer.

However, if you have any of the following in your family, you might want to speak to your GP and be referred to a family cancer clinic:

• three close blood relatives (from the same side of the family) who developed breast or ovarian cancer at any age
• two close relatives (from the same side of the family) who developed breast or ovarian cancer under the age of 60
• one close relative who developed breast cancer under the age of 40
• a case of breast cancer in a male relative
• a relative with cancer in both breasts.

You may find it helpful to read our section on cancer genetics, if you are worried about the risk of developing cancer.