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Table 1 Epidemiology of breast cancer: abbreviated risk factor summary

From: Towards an integrated model for breast cancer etiology: The lifelong interplay of genes, lifestyle, and hormones

Risk factor Direction of effecta
Well-confirmed risk factors  
   Family history in first-degree relative or genetic predisposition (e.g. BRCA1) ↑↑
   Benign breast disease ↑↑
   Mammographically dense breasts ↑↑
   Age at first birth > 30 years versus at < 20 years ↑↑
   Lactation (longer durations)
   Menopause at > 54 years versus at < 45 years ↑↑
   High endogenous estrogen levels ↑↑
   Postmenopausal hormone use
   Ionizing radiation exposure in childhood ↑↑
   Menarche at < 12 years versus at > 14 years
   High body mass index (postmenopausal)
   High body mass index (premenopausal)b
   Alcohol use (~1 or more drinks/day)
Probable relationship exists, based on substantial data  
   Current oral contraceptive use
   Physical activity
Limited study to date  
   High prolactin levels ↑↑
   High premenopausal insulin-like growth factor I levels ↑↑
   In utero exposures
   Nonsteroidal anti-inflammatory drug use
  1. a Arrows indicate approximate magnitude of the relationship: ↑, slight to moderate increase in risk; ↑↑, moderate to large increase in risk; ↓, slight to moderate decrease in risk; ↓↓, moderate to large decrease in risk. b In Western countries – data are less consistent in other lower risk populations.