Investigators have found that residing in areas with high levels of particulate air pollution may be associated with an increased risk of developing breast cancer, according to a recent study published by White et al in the Journal of the National Cancer Institute.
Background
Particulate matter is a mixture of solid particles and liquid droplets found in the air and can originate from numerous sources—including motor vehicle exhaust, combustion processes related to oil and coal, wood smoke and vegetation burning, and industrial emissions. The particulate matter pollution measured in this study was 2.5 µm in diameter or smaller, indicating the particle size able to be inhaled deep into the lungs.
Study Methods and Results
In this study, the investigators used data from the NIH-AARP Diet and Health Study involving more than 500,000 individuals from 1995 to 1996 across six states (California, Florida, Pennsylvania, New Jersey, North Carolina, and Louisiana) and two metropolitan areas (Atlanta and Detroit). The female participants in the study had an average age of 62 years and identified predominantly as non-Hispanic White.
The investigators then estimated the annual average historical particulate matter concentrations for each of the included areas of residence. Although previous studies have neglected past exposures and assessed breast cancer risk only in relation to air pollution around the time of study enrollment, the study investigators were particularly interested in air pollution exposures during a period of 10 to 15 years prior to enrollment in the study—given the length of time it may take for the cancer to develop.
After a follow-up of 20 years, the investigators identified 15,870 cases of breast cancer. They discovered the largest increases in breast cancer incidence were among individuals who had higher average particulate matter concentrations near their residence prior to enrolling in the study, compared with those who lived in areas with lower levels of particulate matter concentrations.
“We observed an 8% increase in breast cancer incidence for living in areas with higher [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,” explained lead study author Alexandra White, PhD, Head of the Environment and Cancer Epidemiology Group at the National Institute of Environmental Health Sciences (NIEHS) at the National Institutes of Health.
To consider how the relationship between air pollution and breast cancer varied by tumor type, the investigators evaluated estrogen receptor (ER)-positive and -negative tumors separately. They uncovered that particulate matter was associated with a higher incidence of ER-positive breast cancer but not ER-negative breast cancer, suggesting that particulate matter may affect breast cancer through an underlying biologic pathway of endocrine disruption.
Conclusions
“The ability to consider historic air pollution levels is an important strength of this research,” emphasized senior study author Rena Jones, PhD, of the National Cancer Institute (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,” she added.
The investigators revealed the study was limited in its ability to explore any differences in the relationship between air pollution and breast cancer across the different study areas. They suggested further studies may be needed to explore how the regional differences in air pollution—including the various types of particulate matter individuals are exposed to—could impact the risk of developing breast cancer.
“These findings add to a growing body of literature suggesting that air pollution is related to breast cancer,” Dr. White concluded.
The investigators noted that individuals can check the air quality and particulate matter concentrations in their areas by visiting airnow.gov.
Disclosure: The research in this study was funded by the NIEHS and NCI Intramural Program. For full disclosures of the study authors, visit academic.oup.com.
