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Built environment and post-menopausal breast cancer risk : analysis of a linked British Columbian cohort Harrigan, Sean Patrick


Background: Breast cancer is the most common type of cancer worldwide and the second leading cause of cancer deaths in women. Up to 50% of breast cancer cases are preventable, underscoring the importance of research into underlying risk factors, especially for post- menopausal women. With urbanization rates increasing in recent decades, the built environment may contain an important yet understudied set of modifiable breast cancer risk factors. Objectives: To evaluate the impact of three factors of the built environment– traffic-related air pollution (TRAP), measured using NO2, walkability, and residential greenness – on risk of breast cancer in post-menopausal women in the Lower Mainland of British Columbia (BC). Methods: This research was conducted using BC Generations Project cohort and linked CANUE environmental datasets. Descriptive statistics summarized socio-demographic, behavioural and health indicators in relation to the built environment. Cox proportional hazard regression was used to model cancer risk for three built environmental factors, while adjusting for relevant confounders. A change-in-effect model building strategy was used. Results: The study included 7,330 participants, including 122 incident breast cancer cases. The HR for a 10-ppb increase in baseline NO₂ was 1.45 (95% CI=0.90, 2.33; p=0.12), whereas the HR for NO₂ averaged over the years 1980-2012 was 1.41 (95% CI=0.95, 2.08; p = 0.09), both adjusting for body mass index and social deprivation. The walkability model had HRs adjusted for social deprivation, ranging from 1.67 to 2.53 for quintile (Q) 2 though Q5 (Q5 being most walkable), with the highest HR being for Q3 (test for trend p=0.05). The HR (unadjusted) for baseline greenness was 0.96 for a 1-interquartile range increase (p=0.76), The HR for greenness averaged over 1982-2016 adjusted for social deprivation was 0.80 (p=0.07). Conclusions: Although statistically non-significant, the magnitude and direction of TRAP HR was similar to previous studies. This study was the first study to our knowledge to assess whether walkability and greenness are associated with breast cancer risk. We found that those residing in less walkable communities; or in neighbourhoods with more greenness had lower risk of breast cancer (statistically non-significant). More research into these associations is warranted.

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