Air pollution exposure may lead to breast cancer

Exposure to high levels of fine particulate matter (PM_2.5) appears to contribute to an increased risk of oestrogen receptor (ER)-positive breast cancer, as shown in a study.

Large data from the NIH-AARP* Diet and Health Study showed that every 10-ug/m³ increase in PM_2.5 exposure was associated with an 8-percent increase in the number of new cases of breast cancer (hazard ratio [HR], 1.08, 95 percent confidence interval [CI], 1.02–1.13). [J Natl Cancer Inst 2023;doi:10.1093/jnci/djad170]

“Although this is a relatively modest increase, these findings are significant given that air pollution is a ubiquitous exposure that impacts almost everyone,” said lead study author Dr Alexandra White who heads the Environment and Cancer Epidemiology Group at the National Institute of Environmental Health Sciences (NIEHS).

Further analysis indicated that the association between fine particulate matter exposure and breast cancer was pronounced for ER-positive tumours (HR, 1.10, 95 percent CI, 1.04–1.17) but not for ER-negative tumours (HR, 0.97, 95 percent CI, 0.84–1.13; p=0.3 for heterogeneity).

In state-specific estimates, meanwhile, were imprecise, the overall breast cancer HRs were >1 across the catchment areas, ranging from 1.26 (95 percent CI, 0.96–1.64) for North Carolina to 1.04 (95 percent CI, 0.68–1.57) for Louisiana (p=0.9 for heterogeneity).

“These findings add to a growing body of literature suggesting that air pollution is related to breast cancer,” White said, adding that PM_2.5 may affect breast cancer through an underlying biologic pathway of endocrine disruption.

The present analysis included 500,000 men and women (average age 62 years) residing in six states (California, Florida, Pennsylvania, New Jersey, North Carolina, and Louisiana) and in two metropolitan areas (Atlanta and Detroit) in the US. A total of 15,870 incident breast cancer cases were documented over approximately 20 years.

White and her team estimated annual average historical PM_2.5 concentrations for each individual’s residence, with a focus on air pollution exposures during a period of 10‒15 years prior to enrolment in the study.

“The ability to consider historic air pollution levels is an important strength of this research,” said senior study author Dr Rena Jones of the National Cancer Institute. “It can take many years for breast cancer to develop and, in the past, air pollution levels tended to be higher, which may make previous exposure levels particularly relevant for cancer development.”

Nevertheless, White and Jones acknowledged that their study was limited in its ability to explore any differences in the relationship between air pollution and breast cancer across the different study areas. The investigators called for additional investigations to explore how the regional differences in air pollution, including the various types of PM_2.5 that women are exposed to, could impact their risk of developing breast cancer.

*The National Institutes of Health and the American Association of Retired Persons