Long-term historical exposure to air pollution is associated with an increased risk of breast cancer, according to research published in the Journal of the National Cancer Institute.
Researchers found an increased risk of invasive breast cancer and estrogen receptor (ER)-positive breast cancer in particular with each 10 μg/m3 increase in fine particulate matter (PM2.5) concentration.
The researchers noted that PM2.5 “has been inconsistently associated with breast cancer incidence, but few studies have considered historic exposure when levels were higher.” Therefore, the researchers analyzed data from patients with PM2.5 exposure during the 1980s and 1990s.
The study included 196,905 women without a prior history of cancer who were enrolled in the prospective NIH-AARP Diet and Health Study in 1995 and 1996. At baseline, the mean age of the cohort was 61.8 years, and 44% of patients were never smokers.
The researchers estimated average PM2.5 levels at patients’ residences each year from 1980 to 2010 but focused mainly on 3 time periods: 1980-1984, 1985-1989, and 1990-1994. The mean PM2.5 concentrations decreased by about 17% over these periods, from 18.70 μg/m3 in 1980-1984 to 15.60 μg/m3 in 1990-1994.
Over a median follow-up of 20.7 years, there were 15,870 breast cancer diagnoses, 92% of them in postmenopausal women (n=14,621).
A 10 μg/m3 increase in PM2.5 was associated with an increase in the risk of breast cancer during 1980-1984 (hazard ratio [HR], 1.08; 95% CI, 1.02-1.13), during 1985-1989 (HR, 1.07; 95% CI, 1.02-1.13), and during 1990-1994 (HR, 1.07; 95% CI, 1.01-1.14).
During 1980-1984, a 10 μg/m3 increase in PM2.5 was associated with an increased risk of invasive breast cancer (HR, 1.08; 95% CI, 1.02-1.14) but not ductal carcinoma in situ (HR, 1.02; 95% CI, 0.90-1.16).
Similarly, a 10 μg/m3 increase in PM2.5 was associated with an increased risk of ER-positive breast cancer (HR, 1.10; 95% CI, 1.04-1.17) but not ER-negative breast cancer (HR, 0.97; 95% CI, 0.84-1.13).
The researchers also found evidence to suggest geographic variations in the association between PM2.5 and breast cancer. For example, the association was lowest for Louisiana (HR, 1.04; 95% CI, 0.68-1.57) and highest for North Carolina (HR, 1.26; 95% CI, 0.96-1.64). However, these analyses were underpowered.
“In this large US cohort with historical air pollutant exposure estimates, PM2.5 was associated with risk of ER-positive breast cancer,” the researchers concluded. “State-specific estimates were imprecise but suggest that future work should consider region-specific associations and the potential contribution of PM2.5 chemical constituency in modifying the observed association.”
White AJ, Fisher JA, Sweeney MR, et al. Ambient fine particulate matter and breast cancer incidence in a large prospective US cohort. J Natl Cancer Inst. Published online September 11, 2023. doi:10.1093/jnci/djad170