Breast cancer: risk factors
Many of the known risk factors for breast cancer relate 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. 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.
Parity The higher the number of full-term pregnancies the greater the protection.
Some risk factors relate to lifestyles / health behaviours:
| Factor | Protective | Increases risk |
|---|---|---|
| Nutrition | Swithching 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. |
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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). |
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