Breast cancer causes and risk factors

Overview

About 44,000 people in the UK each year are diagnosed with breast cancer. The causes of breast cancer are not yet completely understood, but it is known that some factors (known as risk factors| ) may increase a woman’s risk of developing the disease. The risk of developing breast cancer is very small in young women and increases as women get older. Eight out of ten (80%) breast cancers occur in women over the age of 50. Other risk factors include being overweight, having a significant family history of breast cancer, using hormone replacement therapy after the age of 50 or taking the contraceptive pill.

Risk factors

A personal history of breast cancer or certain breast diseases

• Women who have had breast cancer before are at a greater risk of developing a new breast cancer.
• Certain types of benign breast disease – lobular carcinoma in situ (LCIS) or atypical hyperplasia – are associated with an increased risk of breast cancer.

Hormonal factors

As the female hormone oestrogen can affect the development of breast cancer, exposure to oestrogen (without any breaks) over a long period can increase the risk. The following risk factors are related to oestrogen exposure.

• Women who are taking combined hormone replacement therapy (HRT), or have recently taken it, have a slightly increased risk of breast cancer. 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.
• Women who are taking the contraceptive pill, or have recently taken it, have a very slightly increased risk of developing breast cancer.
• Women who don’t have children are slightly more likely to develop breast cancer than women who have children.
• Women who have never breastfed are slightly more likely to develop breast cancer than women who have breastfed for more than a year.
• Women who start their periods at a young age (early puberty) or have a late menopause have a slightly higher risk of breast cancer.

Lifestyle

• Drinking more than two units of alcohol a day over many years can increase the risk. A unit of alcohol is half a pint of normal strength lager or beer, a small glass (125ml) of wine, or a single measure (25ml) of spirit.
• Being overweight, once you have had your menopause, can increase the risk of breast cancer.

Genetics

A very small number – between 5–10% (1 in 20 – 1 in 10) – of breast cancers are thought to be related to faulty genes that run in families. The two main genes linked to breast cancer are BRCA1 and BRCA2. If you have a strong family history| of breast or ovarian cancer, it is possible that you have inherited a faulty cancer gene. But keep in mind that breast cancer is the most common cancer in women in the UK, so even if you have one or even two elderly family members with breast cancer, it is unlikely that you carry one of these gene changes (mutations).

If you are worried about your breast cancer risk, we have more detailed information on breast cancer risk factors| and cancer genetics| .