title: Body size, mammographic density, and breast cancer risk.
abstract: BACKGROUND
  Greater weight and body mass index (BMI) are negatively correlated with mammographic density, a strong risk factor for breast cancer, and are associated with an increased risk of breast cancer in postmenopausal women, but with a reduced risk in premenopausal women. We have examined the associations of body size and mammographic density on breast cancer risk.
  
  
  METHODS
  We examined the associations of body size and the percentage of mammographic density at baseline with subsequent risk of breast cancer among 1,114 matched case-control pairs identified from three screening programs. The effect of each factor on risk of breast cancer was examined before and after adjustment for the other, using logistic regression.
  
  
  RESULTS
  In all subjects, before adjustment for mammographic density, breast cancer risk in the highest quintile of BMI, compared with the lowest, was 1.04 [95% confidence interval (CI), 0.8-1.4]. BMI was associated positively with breast cancer risk in postmenopausal women, and negatively in premenopausal women. After adjustment for density, the risk associated with BMI in all subjects increased to 1.60 (95% CI, 1.2-2.2), and was positive in both menopausal groups. Adjustment for BMI increased breast cancer risk in women with 75% or greater density, compared with 0%, increased from 4.25 (95% CI, 1.6-11.1) to 5.86 (95% CI, 2.2-15.6).
  
  
  CONCLUSIONS
  BMI and mammographic density are independent risk factors for breast cancer, and likely to operate through different pathways. The strong negative correlated between them will lead to underestimation of the effects on risk of either pathway if confounding is not controlled.
authors.affiliation: Campbell Family Institute for Breast Cancer Research, Ontario Cancer Institute, Toronto, Ontario, Canada M5G 2K9. boyd@uhnres.utoronto.ca
authors.forename: Norman F
authors.initials: NF
authors.lastname: Boyd
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Martin
authors.forename: Limei
authors.initials: L
authors.lastname: Sun
authors.forename: Helen
authors.initials: H
authors.lastname: Guo
authors.forename: Anna
authors.initials: A
authors.lastname: Chiarelli
authors.forename: Greg
authors.initials: G
authors.lastname: Hislop
authors.forename: Martin
authors.initials: M
authors.lastname: Yaffe
authors.forename: Salomon
authors.initials: S
authors.lastname: Minkin
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D049628:Body Size; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008327:Mammography / Q000379:methods*; D008403:Mass Screening; D008593:Menopause; D008875:Middle Aged; D015233:Models, Statistical; D012306:Risk; D012307:Risk Factors