2060

Background: Exposure to natural vegetation or “greenness” promotes breast cancer risk-reduction behaviors (e.g. greater physical activity and lower BMI) and three epidemiologic studies reported inverse associations with breast cancer risk; however, it remains unknown whether this is due to direct biological effects on breast tissue or indirect impacts on lifestyle. We examined the association between greenness and mammographic density—a strong risk factor for breast cancer—to determine whether greenness directly influences breast tissue composition. Methods: We included 2,323 women without a history of breast cancer who underwent mammographic screening at the Brigham and Women’s Hospital from 2007-2014. Normalized Difference Vegetation Index (NDVI) satellite data at 1 km² scale at participants’ residential address was used to estimate 5-, 3- and 1-year cumulative average annual and summer greenness prior to the mammogram. We used multivariable linear regression to estimate differences in log transformed volumetric percent density for a 0.1 unit increase in NDVI adjusted for breast density predictors and stratified by menopausal status. Results: Overall, associations were null for NDVI measures and mammographic density. Among 1,108 premenopausal women, 5-year annual average NDVI was non-significantly inversely associated with percent mammographic density (β=-0.01 95% CI -0.03, 0.02; p-value=0.52) after adjustment for age, BMI, race/ethnicity, parity, family history of breast cancer, and benign breast disease; results were similar for other NDVI measures. Among 1,215 postmenopausal women, 5-year annual average NDVI was non-significantly inversely associated with percent mammographic density (β=-0.02 95% CI -0.04, 0.01; p-value=0.18) after adjustment for aforementioned variables and hormonal therapy use; results were similar for other NDVI measures.Conclusions: While in the expected direction, findings suggest that greenness does not have a direct role on breast tissue composition. Future work will explore if the potential benefit of greenness is more relevant to subgroups of women based on race/ethnicity, BMI, and physical activity.