Mapping the risk of breast cancer to exposure from traffic-related air pollution using land-use regression in Vancouver, BC
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An environmental role in breast cancer etiology has been suspected but evidence is still inconclusive. Traffic-related air pollution is a potentially modifiable risk factor that has been studied in the etiology of breast cancer. Two Canadian studies using similar methodology to this study have recently reported positive associations between exposure to nitrogen dioxide (NO2), a proxy for traffic-related air pollution, and breast cancer. This thesis used land-use regression to estimate NO2 exposure for 2,015 women recruited from Vancouver, British Columbia (BC) into a population-based case-control study conducted in 2005-2010. Cases were recruited from the BC Cancer Agency and controls from the Screening Mammography Program of BC. Cross-sectional and historical analyses were conducted using NO2 estimated at time of study entry and ten years prior to study entry, respectively. Logistic regression models were created to estimate the relationship between exposure to NO2 and breast cancer, adjusting for breast cancer risk factors and stratified by menopausal status. Sensitivity analyses were conducted, assessing potential biases introduced by screening mammography program attendance and immigrant status, among others. The analysis at study entry included 964 cases and 945 controls. No association between NO2 exposure (per 5 ppb increases) and risk of breast cancer was observed in the postmenopausal sample at study entry or at ten years prior to study entry. A consistent positive association in premenopausal women was observed at study entry (OR=1.17, 95% CI: 0.93, 1.48) and ten years prior to study entry (OR=1.18, 95% CI: 0.93, 1.49). The association between historical estimates of NO¬2 (per 5 ppb increases) and breast cancer was stronger in a sensitivity analysis excluding cases who had not attended screening mammography in the premenopausal sample (OR=1.20, 95% CI: 0.91, 1.59). This study adds to the growing literature on exposure to traffic-related air pollution and breast cancer incidence. The results provide some support for the hypothesis that increased exposure may be associated with breast cancer, particularly in premenopausal women, although bias may have been introduced due to the selection of controls from a screening mammography program and low response rates. Future research, especially using prospective cohort studies, is needed.