Long-term Exposure to Fine Particulate Matter and Breast Cancer Incidence in the Danish Nurse Cohort Study

Abstract

<b>Background:</b> An association between air pollution and breast cancer risk has been suggested, but evidence is sparse and inconclusive.<b>Methods:</b> We included 22,877 female nurses from the Danish Nurse Cohort who were recruited in 1993 or 1999 and followed them for incidence of breast cancer (<i>N</i> = 1,145) until 2013 in the Danish Cancer Register. We estimated annual mean concentrations of particulate matter with diameter <2.5 μg/m³ (PM_2.5) and <10 μg/m³ (PM₁₀), and nitrogen dioxide (NO₂) at nurses' residences since 1990 using an atmospheric chemistry transport model. We examined the association between the 3-year running mean of each pollutant and breast cancer incidence using a time-varying Cox regression.<b>Results:</b> We found no association between breast cancer and PM_2.5 (HR, 0.99; 95% confidence interval, 0.94-1.10 per interquartile range of 3.3 μg/m³), PM₁₀ (1.02; 0.94-1.10 per 2.9 μg/m³), or NO₂ (0.99; 0.93-1.05 per 7.4 μg/m³).<b>Conclusions:</b> Air pollution is not associated with breast cancer risk.<b>Impact:</b> Exposure to air pollution in adulthood does not increase the risk of breast cancer, but more data on the effects of early exposure, before first birth, are needed. <i>Cancer Epidemiol Biomarkers Prev; 26(3); 428-30. ©2016 AACR</i>.