title: Positive association between mammographic breast density and bone mineral density in the Postmenopausal Estrogen/Progestin Interventions Study.
abstract: BACKGROUND
  Mammographic breast density is a strong independent risk factor for breast cancer. We hypothesized that demonstration of an association between mammographic breast density and bone mineral density (BMD) would suggest a unifying underlying mechanism influencing both breast density and BMD.
  
  
  METHODS
  In a cross-sectional analysis of baseline data from the Postmenopausal Estrogen/Progestin Interventions Study (PEPI), participants were aged 45 to 64 years and were at least 1 year postmenopausal. Mammographic breast density (percentage of the breast composed of dense tissue), the outcome, was assessed with a computer-assisted percentage-density method. BMD, the primary predictor, was measured with dual-energy X-ray absorptiometry. Women quitting menopausal hormone therapy to join PEPI were designated recent hormone users.
  
  
  RESULTS
  The mean age of the 594 women was 56 years. The average time since menopause was 5.6 years. After adjustment for age, body mass index, and cigarette smoking, in women who were not recent hormone users before trial enrollment (n = 415), mammographic density was positively associated with total hip (P = 0.04) and lumbar (P = 0.08) BMD. Mammographic density of recent hormone users (n = 171) was not significantly related to either total hip (P = 0.51) or lumbar (P = 0.44) BMD. In participants who were not recent hormone users, mammographic density was 4% greater in the highest quartile of total hip BMD than in the lowest. In participants who were not recent hormone users, mammographic density was 5% greater in the highest quartile of lumbar spine BMD than in the lowest.
  
  
  CONCLUSIONS
  Mammographic density and BMD are positively associated in women who have not recently used postmenopausal hormones. A unifying biological mechanism may link mammographic density and BMD. Recent exogenous postmenopausal hormone use may obscure the association between mammographic density and BMD by having a persistent effect on breast tissue.
authors.affiliation: Division of General Internal Medicine, David Geffen School of Medicine at University of California, Los Angeles, CA, USA. ccrandall@mednet.ucla.edu
authors.forename: Carolyn
authors.initials: C
authors.lastname: Crandall
authors.forename: Shana
authors.initials: S
authors.lastname: Palla
authors.forename: Beth A
authors.initials: BA
authors.lastname: Reboussin
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.forename: Gail A
authors.initials: GA
authors.lastname: Greendale
mesh_terms: D015519:Bone Density; D001940:Breast / Q000033:anatomy & histology*; D003430:Cross-Sectional Studies; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D008327:Mammography / Q000706:statistics & numerical data*; D008875:Middle Aged; D017698:Postmenopause; D012016:Reference Values; D012307:Risk Factors