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

Background: An association between air pollution and breast cancer risk has been suggested, but evidence is sparse and inconclusive.
Methods: 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 (N = 1,145) until 2013 in the Danish Cancer Register. We estimated annual mean concentrations of particulate matter with diameter <2.5 μg/m3 (PM2.5) 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.
Results: We found no association between breast cancer and PM2.5 (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).Conclusions: Air pollution is not associated with breast cancer risk.Impact: 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. Cancer Epidemiol Biomarkers Prev; 26(3); 428-30. ©2016 AACR. ©2016 American Association for Cancer Research.