4.3 Risk factors

Table 4.2 Risk factors for breast cancer, by direction of association and strength of evidence


Increases risk

Decreases risk

Convincing or probable

Family history of breast cancer1,2



Nulliparity and low parity2,3

Physical activity18


Late age at first pregnancy2,3

Greater body fat (pre-menopausal cancer)18


Late natural menopause2,3

Tamoxifen and raloxifene5,20,21


Early menarche2,3


Oral contraceptives4,5


Hormone replacement therapy5




Greater body fatness, abdominal fatness and weight gain in adulthood (post-menopausal cancer)7,8,9






Ionizing radiation12, 13


Benign breast disease14


High socio-economic status15


Red meat (pre-menopausal cancer)16,17

Dairy food22


Higher (own) birthweight 17

Isoflavones from soya foods23

Vitamin D24,25,26

Dietary fibre27

Aspirin and other non-steroidal anti-inflammatory drugs28,29

1 First degree relative(s) with breast cancer; 2 Veronesi et al., 2005; 3 Key et al., 2001; 4 combined oestrogen-progestogen formulations; 5 International Agency for Research on Cancer, 2011a; 6 exposure during pregnancy; 7 World Cancer Research Fund / American Institute for Cancer Research, 2007; 8 Suzuki et al., 2009; 9 Vrieling et al., 2010; 10 Suzuki et al., 2008; 11 Secretan et al., 2009; 12 El Ghissassi et al., 2009; 13 Jansen-van der Weide et al., 2010; 14 Zhou et al., 2011; 15 Faggiano et al., 1997; 16 Taylor et al., 2009; 17 Xu et al., 2009; 18 International Agency for Research on Cancer, 2002; 19 Collaborative Group on Hormonal Factors in Breast Cancer, 2002; 20 in pre-menopausal women at high breast cancer risk; 21 Wickerham et al., 2009; 22 Dong et al., 2011a;

23 Dong & Qin, 2011; 24 intake and blood levels; 25 Chen et al., 2010; 26 Yin et al., 2010; 27 Dong et al., 2011b; 28 Takkouche et al., 2008; 29 Zhao et al., 2009

Breast cancer is a heterogeneous disease, comprising several distinct subgroups defined on the basis of hormonal receptor status and/or morphology. Recently interest has grown in distinguishing between risk factors for different subtypes (see, for example, Suzuki et al., 2008; Reeves et al., 2009; Suzuki et al., 2009; Vrieling et al., 2010; Yang et al., 2011). Up to 10% of breast cancer cases are hereditary and a woman's chance of developing the disease is increased if any of her first degree female relatives had breast cancer, particularly if more than one relative was affected at a young age (Veronesi et al., 2005). By age 70, women who carry BRCA1 gene mutations have a 65% chance of developing breast cancer, while those who carry BRCA2 mutations have a 45% risk (Antoniou et al., 2003). Family history may interact with other factors to modify risk, for example, exposure to low doses of radiation such as x-rays (Jansen-van der Weide et al., 2010) or history of benign breast disease (Zhou et al., 2011). Other than genetic factors, the major determinant of breast cancer risk is lifetime exposure to oestrogen (Table 4.2). Higher endogenous oestrogen exposure, as well as exogenous oestrogens, increases risk. In contrast, in pre-menopausal women at high risk of breast cancer, the anti-oestrogenic drugs tamoxifen and raloxifene reduce the chances of developing the disease by about half. 

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