High Levels of Particulate Air Pollution Linked to Increased Incidence of Breast Cancer

Areas with high levels of particulate air pollution may be associated with an increased incidence of breast cancer, according to a recent study published in the Journal of the National Cancer Institute.

“We observed an eight percent increase in breast cancer incidence for living in areas with higher [fine particulate matter] exposure. Although this is a relatively modest increase, these findings are significant given that air pollution is a ubiquitous exposure that impacts almost everyone,” said Alexandra White, PhD, lead author and head of the Environment and Cancer Epidemiology Group at the National Institute of Health Sciences (NIEHS). “These findings add to a growing body of literature suggesting that air pollution is related to breast cancer.” 

The study was conducted by researchers from NIEHS and the National Cancer Institute (NCI), both part of the National Institutes of Health (NIH). Using information from the NIH-AARP Diet and Health Study, which documented breast cancer cases in over 500,000 men and women from across the country between 1995 and 1996, researchers aimed to compare breast cancer incidence to the participant's level of particulate matter exposure.

According to the study, particulate matter is a combination of solid particulates and liquid droplets found in the air that come from various sources, such as motor vehicle exhaust and industrial emissions. This study measured particulate matter pollution as 2.5 microns in diameter or smaller (PM_2.5), which is small enough to be inhaled deep into the lungs.

Researchers focused on the women within the NIH-AARP Diet and Health Study cohort, most of whom identified as white and averaged about 62 years in age. The women were followed for 20 years, and 15,870 cancer cases were identified. The women's annual average historical PM_2.5 concentrations were estimated according to each participant's residence. Researchers were particularly interested in their exposure level 10 to 15 years before their enrollment in the study due to the time it takes for some cancers to develop.

“The ability to consider historic air pollution levels is an important strength of this research,” said Rena Jones, PhD, senior author and principal investigator of the study at NCI. “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.”

To differentiate how air pollution impacted different types of breast cancer tumors, researchers observed estrogen receptor-positive (ER+) and -negative (ER-) tumors separately. The analysis showed that PM_2.5 was associated with a higher incidence of ER+ breast cancer tumors, the most common tumors diagnosed among women in the US, but not ER- tumors, according to the study.

These results indicate that PM_2.5 may impact breast cancer through an underlying biological pathway of endocrine disruption, the authors explained. Future research, they said, should investigate the regional differences in air pollution and how different types of PM_2.5 could impact a woman’s risk of developing breast cancer.