title: Association between air pollution and mammographic breast density in the Breast Cancer Surveilance Consortium.
abstract: Mammographic breast density is a well-established strong risk factor for breast cancer. The environmental contributors to geographic variation in breast density in urban and rural areas are poorly understood. We examined the association between breast density and exposure to ambient air pollutants (particulate matter <2.5 μm in diameter (PM2.5) and ozone (O3)) in a large population-based screening registry.
  
  
  
  Participants included women undergoing mammography screening at imaging facilities within the Breast Cancer Surveillance Consortium (2001-2009). We included women aged ≥40 years with known residential zip codes before the index mammogram (n = 279,967). Breast density was assessed using the American College of Radiology's Breast Imaging-Reporting and Data System (BI-RADS) four-category breast density classification. PM2.5and O3estimates for grids across the USA (2001-2008) were obtained from the US Environmental Protection Agency Hierarchical Bayesian Model (HBM). For the majority of women (94%), these estimates were available for the year preceding the mammogram date. Association between exposure to air pollutants and density was estimated using polytomous logistic regression, adjusting for potential confounders.
  
  
  
  Women with extremely dense breasts had higher mean PM2.5and lower O3exposures than women with fatty breasts (8.97 vs. 8.66 ug/m3and 33.70 vs. 35.82 parts per billion (ppb), respectively). In regression analysis, women with heterogeneously dense vs. scattered fibroglandular breasts were more likely to have higher exposure to PM2.5(fourth vs. first quartile odds ratio (OR) = 1.19, 95% confidence interval (CI) 1.16 - 1.23). Women with extremely dense vs. scattered fibroglandular breasts were less likely to have higher levels of ozone exposure (fourth vs. first quartile OR = 0.80, 95% CI 0.73-0.87).
  
  
  
  Exposure to PM2.5and O3may in part explain geographical variation in mammographic density. Further studies are warranted to determine the causal nature of these associations.
authors.affiliation: Department of Epidemiology, College of Public Health and Health Professions and College of Medicine, University of Florida, 2004 Mowry Rd, Gainesville, FL, 32610, USA. lyaghjyan@ufl.edu.
authors.forename: Lusine
authors.initials: L
authors.lastname: Yaghjyan
authors.affiliation: Group Health Research Institute, 1730 Minor Ave, Seattle, WA, 98101, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Arao
authors.affiliation: Department of Environmental Health, University of Cincinnati, 3223 Eden Ave, Cincinnati, OH, 45267, USA.|Division of Biostatistics and Epidemiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH, 45229, USA.
authors.forename: Cole
authors.initials: C
authors.lastname: Brokamp
authors.affiliation: Group Health Research Institute, 1730 Minor Ave, Seattle, WA, 98101, USA.
authors.forename: Ellen S
authors.initials: ES
authors.lastname: O'Meara
authors.affiliation: Department of Surgery, University of Vermont, 111 Colchester Avenue, Burlington, VT, 05401, USA.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Sprague
authors.affiliation: Department of Biostatistics, College of Public Health and Health Professions and College of Medicine, University of Florida, 2004 Mowry Rd, Gainesville, FL, 32610, USA.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Ghita
authors.affiliation: Division of Biostatistics and Epidemiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH, 45229, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Ryan
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000393:Air Pollutants; D000397:Air Pollution; D001940:Breast / Q000473:pathology; D000071060:Breast Density; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology* / Q000473:pathology; D005260:Female; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D016017:Odds Ratio; D011159:Population Surveillance; D012307:Risk Factors; D014481:United States / Q000453:epidemiology
chemical_list: D000393:Air Pollutants
keywords: Air pollution; Breast density; Geographic disparities; Particulate matter