Residential exposure to vehicular traffic-related air pollution during childhood and breast cancer risk

Background: Some studies have supported an association between traffic-related air pollution exposure and breast cancer risk. However, few studies have considered exposures in early life, which may be a period of increased susceptibility. Objectives: To examine the association of childhood residential exposure to traffic-related air pollution with breast cancer development. Methods: The Sister Study is a prospective cohort of 50,884 initially breast cancer-free women, of whom 42,934 provided information at enrollment about roads and traffic near their primary childhood residence before age 14 as well as relevant covariates. Adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) for the association between traffic-related measures at childhood residence and adult incident breast cancer were estimated using Cox regression. Results: During follow-up (mean = 6.3 years), 2,028 breast cancers were diagnosed. Traffic-related characteristics were not consistently associated with breast cancer risk. However, incidence was elevated among women who reported a median/barrier dividing either their primary childhood residential road (aHR = 1.2; 95% CI: 0.9-1.7) or the nearest cross-street (aHR = 1.3; 95% CI: 0.9-1.8, if the cross -street was within 100 ft.), and among women whose nearest cross-street had the highest traffic, >= 3 lanes, and/or a median/barrier (aHR = 1.4; 95% CI: 1.0-1.9). Conclusions: Measures of potential exposure to vehicular traffic were not consistently associated with breast cancer risk. However, living during childhood on or near a road with a median or other barrier, which may be a more easily remembered road characteristic than the others assessed, was associated with increased breast cancer risk.