Abstract 3430: Association of PM2.5 and ozone exposure with mammographic breast density in the Breast Cancer Surveillance Consortium
Authors: Yaghjyan Lusine , Arao Robert , Brokamp Cole , O’Meara Ellen , Sprague Brian , Ghita Gabriela , Ryan Patrick 
Published: July 2016

Abstract
Background: Mammographic breast density (BD) is a well-established and strong breast cancer risk factor. Some studies suggest geographical disparities in BD. Environmental factors such as air pollution may contribute to geographic variation in BD because urban and rural areas have distinct air pollution patterns and some of the pollutants are known to have endocrine disrupting properties. We examined the association of BD with particles&lt;2.5 μm in diameter (PM2.5) and ozone (O3) in a large population-based cohort.
Methods: Women were selected from participants of the Breast Cancer Surveillance Consortium (2001-2009). We included women aged ≥40 years with no history of breast cancer, with BD data available from screening mammography and with known residential zip code for at least 3 years prior to the index mammogram. Categorical BD was defined with BI-RADS breast density classification as predominantly fat, fat with some fibroglandular tissue (reference), heterogeneously dense, and extremely dense. PM2.5 and O3 estimates for grids across the United States from 2001-2008 were obtained from the US Environmental Protection Agency hierarchical Bayesian model (HBM), which combines monitoring data with numerical output from the Community Multi-scale Air Quality model. For both pollutants, the smallest grids available for each year were used. Daily concentrations of PM2.5 and O3 were used to calculate annual concentrations for each grid. Yearly mean exposures of PM2.5 and O3 for each subject were calculated using the inverse distance weighted method based on their zip code centroid and HBM grid centroids. PM2.5 and O3 exposures were modeled as continuous and as quartiles. Associations of PM2.5 and ozone with BD were estimated with polychotomous logistic regression adjusting for potential confounders.
Results: In this study of 368,302 women, participants with extremely dense breasts had mean PM2.5 and O3 exposures of 9.41ug/m3 and 33.76 ug/m3 as compared to 9.02 ug/m3 and 35.42 ug/m3 in women with fatty breasts, respectively. In multivariate regression, women with heterogeneously dense vs. scattered fibroglandular breasts were more likely to have been exposed to higher concentrations of PM2.5 (4th vs. 1st quartile Odds Ratio [OR] = 1.21, 95% Confidence Interval [CI] 1.17-1.24; 3rd vs. 1st quartile: OR = 1.27, 95% CI 1.23-1.30) and women with fatty breasts were less likely to have been exposed to high PM2.5 levels (4th vs. 1st quartile: OR = 0.95, 95% CI 0.91-1.00; 3rd vs. 1st quartile: OR = 0.75, 95% CI 0.73-0.78). Women with heterogeneously and extremely dense vs. scattered fibroglandular breasts were less likely to have been exposed to higher levels of ozone (4th vs. 1st quartile: OR = 0.94, 95% CI 0.89-0.98 and OR = 0.79, 95% CI 0.72-0.86, respectively).
Conclusion: Exposure to PM2.5 and ozone may in part explain geographical variation in BD. Further studies are warranted to determine the causal nature of these associations.
Citation Format: Lusine Yaghjyan, Robert Arao, Cole Brokamp, Ellen O’Meara, Brian Sprague, Gabriela Ghita, Patrick Ryan. Association of PM2.5 and ozone exposure with mammographic breast density in the Breast Cancer Surveillance Consortium. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3430.