Researchers observed an 8% increase in breast cancer incidence for people living in areas with higher PM2.5 exposure

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Residing in an area with high levels of particulate matter of 2.5 microns or smaller (PM2.5) pollution is associated with increased breast cancer risk, found a new study.

The findings of the study conducted by the National Institute of Environmental Health Sciences (NIEHS) and the National Cancer Institute (NCI) across the US were published on the National Institute of Health (NIH) website on September 11, 2023.

The researchers estimated the annual mean historical PM2.5 concentrations for each participant’s residence. “This type of particulate matter is small enough to breathe deep into the lungs.”

Women exposed to higher PM2.5 levels before enrolling in the study had a higher average incidence of breast cancer, the researchers stated. 

They analysed the NIH-American Association of Retired Persons Diet and Health Study data of 500,000 participants who lived in six states (California, Florida, Pennsylvania, New Jersey, North Carolina and Louisiana) and in two metropolitan areas (Atlanta and Detroit) between 1995-1996.

The mean age of participants was 62 years, with most being non-Hispanic White. Some 15,870 cases of breast cancer have been reported over the last 20 years, according to the findings.

“We observed an 8 per cent increase in breast cancer incidence for living in areas with higher PM2.5 exposure, said Alexandra White, lead author and head of the Environment and Cancer Epidemiology Group at NIEHS.

Although this is a relatively modest increase, these findings are significant given that air pollution is a ubiquitous exposure that impacts almost everyone, White added.

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

The ability to consider historic air pollution levels is an important strength of this research, said Rena Jones, 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.”

The report acknowledged its limited ability to investigate the differences in the association between air pollution and breast cancer across study areas. It recommended future studies to explore how regional differences in air pollution impact breast cancer incidence.

To consider how the relationship between air pollution and breast cancer varied by the type of tumour, the researchers evaluated estrogen receptor-positive (ER+) and -negative (ER-) tumours separately.

They found that PM2.5 was associated with a higher incidence of ER+ breast cancer but not ER- tumours. This suggests that PM2.5 may affect breast cancer through an underlying biological pathway of endocrine disruption. ER+ tumours are the most common tumours diagnosed among women in the US.

PM2.5 sources and concentrations may vary significantly across locations due to distinct climatic conditions, emission sources and dispersion patterns.

The sources can be either natural or anthropogenic. Depending on the location, different sources such as vehicle traffic, dust resuspension, biomass burning, power plants, sea salt, industrial emissions, ship emissions and aircraft emissions may contribute to PM2.5 levels.

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