Breast cancer in women - risk factors and causes
The exact cause of breast cancer is unknown. But certain things called risk factors can increase a woman’s chances of developing it. Having one or more risk factors doesn’t mean you will definitely get cancer. Equally, if you don’t have any risk factors, it doesn’t mean you won’t get breast cancer.
Breast cancer is likely to be caused by a combination of different risk factors rather than just one.
The strongest risk factor for breast cancer is increasing age. About 8 out of 10 women diagnosed (80%) are over 50.
Nearly half of all breast cancers (45%) are in women over 65.
Breast cancer and some breast conditions
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Having breast cancer or some breast conditions before can increase your risk of breast cancer. For example, if you have, or have had the following, your risk may increase:
Radiotherapy to the chest at a young age
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Radiotherapy to the chest to treat Hodgkin lymphoma can increase the risk of breast cancer.
Your exposure to the hormones oestrogen and progesterone can affect your breast cancer risk. Factors that can increase risk include:
Taking hormone replacement therapy (HRT) – this can increase your risk, particularly if you’re taking combined HRT (oestrogen and progesterone). When you stop taking HRT, your risk reduces again.
Not having children or having them after the age of 30.
Not having breastfed or breastfeeding for less than a year in total.
Starting your periods early (under the age of 12) or having a late menopause (after the age of 50).
Taking the contraceptive pill, although the risk reduces if you stop taking it.
The following lifestyle factors may slightly increase your breast cancer risk:
Drinking alcohol increases your risk of developing breast cancer.
The increase in risk is small for women who drink within the recommended guidelines.
Being overweight, particularly after the menopause, increases the risk of breast cancer. This may be because it changes the levels of hormones in the body.
Smoking heavily over many years, especially if you started smoking at a young age, can increase your risk.
Family history and risk
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Most women who get breast cancer don’t have a family history of it. If you have just one female relative who has been diagnosed with breast cancer over the age of 40, your risk is unlikely to be very different from other women the same age as you.
But, sometimes breast cancer can run in families.
In general, the chance of there being a family link is greater when:
a number of family members have been diagnosed with breast cancer or related cancers, such as ovarian cancer
the family members are closely related
they were diagnosed at a younger age.
Only a very small proportion of women with breast cancer (5–10%) have a breast cancer gene that greatly increases the risk of breast cancer. The two genes most often found in hereditary breast cancer are called BRCA1 and BRCA2.
We have more information about cancer genetics and breast cancer, which you might find helpful.
Wendy talks about the genetic testing she had, and how it affected her and her family.
Online risk assessment
Our website has an interactive software program called OPERA (Online Personal Education and Risk Assessment) that gives you support and personalised information about inherited breast cancer risk. OPERA isn’t intended to take the place of professional genetic counselling services. If you’re concerned about genetic risk, you should consult your doctor.