Breast cancer: risk factors

Risk factors related to a woman's reproductive history and to oestrogens in the body:

Factor Protective Increases risk
Age at menarche   Early age at menarche (onset of menstrual periods).
Age at menopause   Late menopause.
Age at first full pregnancy The younger a woman begins childbearing the lower her risk.  
Parity The higher the number of full-term pregnancies the greater the protection.  
Breastfeeding Women who breastfeed reduce their risk. The longer a woman breastfeeds the greater the protection.  
Hormone replacement therapy (HRT)   HRT use increases risk and risk increases with duration of use.
Oral contraceptive use   Slightly increases risk in current and recent users.


Risk factors related to  lifestyles / health behaviours:

Factor Protective Increases risk
Nutrition Switching from a high fat / low vegetable diet to a lower fat / higher vegetable diet may reduce risk. Fat intake may cause a small increase in risk.
Bodyweight   Overweight and obesity moderately increases the risk of postmenopausal breast cancer.
Alcohol   Alcohol consumption is associated with increased risk.
Exercise Physical activity has a protective effect.  


Other risk factors include:

Factor Protective Increases risk
Ionising radiation   Ionising radiation is an established risk factor and excessive exposure should be avoided. The risk is stongly related to age at exposure and the younger the age the greater the excess risk.
Benign disease   Some types of benign breast disease increase the risk of developing malignant breast cancer.
Family history   Around 5% of breast cancers are due to inherited genetic factors. In particular, the risk of breast cancer is greatly increased in carriers of mutations of several high-penetrance genes, in particular BRCA1, BRCA2 and p53 (accounting for around 2-5% of cases).