High levels of particulate air pollution associated with increased breast cancer incidence

The researchers saw that the largest increases in breast cancer incidence was among women who on average had higher particulate matter levels (PM2.5) near their home prior to enrolling in the study, compared to those who lived in areas with lower levels of PM2.5.

High levels of particulate air pollution associated with increased breast cancer incidence. Photo: Vladyslav Lytvyshchenko/Unsplash

Particulate matter is a mixture of solid particles and liquid droplets found in the air. It comes from numerous sources, such as motor vehicle exhaust, combustion processes (e.g., oil, coal), wood smoke/vegetation burning, and industrial emissions.

The particulate matter pollution measured in this study was 2.5 microns in diameter or smaller (PM2.5), meaning the particles are small enough to be inhaled deep into the lungs.

“We observed an 8% increase in breast cancer incidence for living in areas with higher PM2.5 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, Ph.D., lead author and head of the Environment and Cancer Epidemiology Group at NIEHS.

“These findings add to a growing body of literature suggesting that air pollution is related to breast cancer.”

The researchers estimated annual average historical PM2.5 concentrations for each participant’s residence.

They were particularly interested in air pollution exposures during a period of 10-15 years prior to enrollment in the study, given the length of time it takes for some cancers to develop.

Most previous studies have assessed breast cancer risk in relation to air pollution around the time of study enrollment and did not consider past exposures.

“The ability to consider historic air pollution levels is an important strength of this research,” said Rena Jones, Ph.D., 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 consider how the relationship between air pollution and breast cancer varied by the type of tumor, the researchers evaluated estrogen receptor-positive (ER+) and -negative (ER-) tumors separately.

They found that PM2.5 was associated with a higher incidence of ER+ breast cancer, but not ER-, tumors. This suggests that PM2.5 may affect breast cancer through an underlying biologic pathway of endocrine disruption. (National Institutes of Health)

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