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What causes breast cancer?

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A cancerous tumour starts from one abnormal cell. The exact reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply 'out of control'.

Risk factors

Although breast cancer can develop for no apparent reason, there are certain 'risk factors' which increase the chance that breast cancer will develop. These include:

Ageing. The risk of developing breast cancer roughly doubles for every 10 years of age. Around 80% of cases develop in women over the age of 50.
Family history. This means close relatives who have or have had breast cancer. In particular, if they were under the age of 50 when diagnosed.

If you have had a previous breast cancer.
Being childless, or if you had your first child after the age of thirty.
Early age of starting periods.
Having a menopause over the age of 55.
Taking HRT (hormone replacement therapy). Taking the combined contraceptive pill may increase the risk slightly.
A past history of some benign breast diseases.
Lifestyle factors: taking little exercise, obesity after the menopause, and excess alcohol.

Family history and genetic testing

About 1 in 20 breast cancers are caused by a 'faulty gene' which can be inherited. Breast cancer which is linked to a faulty gene most commonly affects women in their 30s and 40s. If you have a strong family history of breast cancer you may wish to discuss this with your doctor. Genetic testing to see if you have inherited certain 'faulty genes' is possible. Alternatively contact the National Hereditary Breast Cancer Helpline (details at the end of the leaflet).

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