Additive effects of 10-year exposures to PM_2.5and NO₂and primary cancer incidence in American older adults

Background: Epidemiologic evidence on the relationships between air pollution and the risks of primary cancers other than lung cancer remained largely lacking. We aimed to examine associations of 10-year exposures to fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) with risks of breast, prostate, colorectal, and endometrial cancers. Methods: For each cancer, we constructed a separate cohort among the national Medicare beneficiaries during 2000 to 2016. We simultaneously examined the additive associations of six exposures, namely, moving average exposures to PM_2.5and NO₂over the year of diagnosis and previous 2 years, previous 3 to 5 years, and previous 6 to 10 years, with the risk of first cancer diagnosis after 10 years of follow-up, during which there was no cancer diagnosis. Results: The cohorts included 2.2 to 6.5 million subjects for different cancers. Exposures to PM_2.5and NO₂were associated with increased risks of colorectal and prostate cancers but were not associated with endometrial cancer risk. NO₂was associated with a decreased risk of breast cancer, while the association for PM_2.5remained inconclusive. At exposure levels below the newly updated World Health Organization Air Quality Guideline, we observed substantially larger associations between most exposures and the risks of all cancers, which were translated to hundreds to thousands new cancer cases per year within the cohort per unit increase in each exposure. Conclusions: These findings suggested substantial cancer burden was associated with exposures to PM_2.5and NO₂, emphasizing the urgent need for strategies to mitigate air pollution levels.