Long-term PM2.5 exposure before diagnosis is associated with worse outcome in breast cancer.

PURPOSE Increasingly epidemiological evidence supports that environmental factors are associated with breast cancer (BC) outcomes after a BC diagnosis. Although evidence suggests that air pollution exposure is associated with higher mortality in women with BC, studies investigating potential mechanisms have been lacking. METHODS We evaluated women with BC (N = 151) attended at the National Cancer Institute-Mexico from 2012 to 2015. We calculated 1-year average exposures to particulate matter < 2.5 μm (PM2.5) at home address before diagnosis. We used linear and logistic regression models to determine the associations between PM2.5 exposure and BC aggressiveness (tumor size, molecular phenotype). RESULTS Average annual PM2.5 exposure of this population was 23.0 μg/m3 [standard deviation (SD)]: 1.90 μg/m3]. PM2.5 levels were positively correlated with tumor size at diagnosis (r = 0.22; p = 0.007). Multivariable linear models had a similar inference [risk ratio (RR): 1.32; 95% confidence interval (95% CI): 1.04, 1.674]. We did not observe differences in this association by age or menopause status. Further, women with triple-negative BC (TNBC) had significantly higher PM2.5 levels compared with other phenotypes (p = 0.015). Multivariable-adjusted logistic regression models assessing the association between PM2.5 and tumor size had a similar inference (RR 1.41; 95% CI 1.05, 1.89) overall for all ages and also for women who were ≤ 50 years old at diagnosis (RR 1.63; 95% CI 1.036, 2.57). CONCLUSIONS Our findings suggest a significant association between long-term PM2.5 exposure and BC aggressiveness based on tumor size and phenotype, as well as a worse outcome.