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Air pollution may increase risk for greater breast density
Living in an area with high levels of fine particles from air pollution may increase a woman’s chance of having dense breasts, a risk factor for breast cancer, according to study results published in Breast Cancer Research.
Conversely, researchers found that women exposed to higher ozone concentrations have a lower chance of having dense breasts.
“We found a positive association between fine particle concentration exposure and breast density, but an inverse association between ozone exposure and breast density,” Lusine Yaghjyan, MD, MPH, PhD, an assistant professor in the department of epidemiology at University of Florida, said in a press release. “This is an intriguing result that warrants further investigation to unpick any possible biological mechanism that might cause ozone exposure to reduce a woman’s chance of having dense breasts.”
Previous studies suggest women living in urban areas may have higher breast density compared with those living in rural environments. Although some air pollutants are known to have endocrine-disrupting properties, researchers noted these differences may have been confounded by varying BMI levels.
To further study the association between air pollution and mammographic breast density, researchers examined 279,967 women aged 40 years or older (mean age, 57 years; range, 40-102) who received screening mammograms between 2001 and 2009 and had no history of breast cancer. The majority of women (70.9%) were postmenopausal, and more lived in urban areas (60.3%) than rural areas (39.7%).
Researchers defined each woman’s breast density using the American College of Radiology’s Breast Imaging-Reporting and Data System, which divides breast density into four categories: predominantly fat (category I; 10.8% of the women), fat with some fibroglandular tissue (category II; 41.7%), heterogeneously dense (category III; 39.4%) and extremely dense (category IV; 8.2%).
Researchers also measured participants’ exposure to ambient air pollutants — or particulate matter less than 2.5 µm in diameter (PM2.5) and ozone (O3) — using 2001 to 2008 grid estimates from the U.S. Environmental Protection Agency Hierarchical Bayesian Model.
Overall, women with extremely dense breasts had higher mean PM2.5 exposures (8.97 ug/m3 vs. 8.66 ug/m3) and lower O3 exposures (33.7 parts per billion [ppb] vs. 35.82 ppb) than women with fatty breasts.
Multivariate regression analysis showed women with category III vs. category II density were more likely to have been exposed to higher PM2.5 concentrations (OR for fourth vs. first quartile = 1.19; 95% CI, 1.16-1.23), whereas women with category I density were less likely to have been exposed to higher PM2.5 levels (OR = 0.88; 95% CI, 0.85-0.92).
For every one-unit increase in PM2.5 concentration, a women’s likelihood of having dense breasts increased 4% and her likelihood of having fatty breasts decreased 2%.
Women with category IV density vs. category II density were less likely to be exposed to higher O3 concentrations (OR for fourth vs. first quartile = 0.8; 95% CI, 0.73-0.87), whereas likelihood increased among women with category I density (OR for forth vs. first quartile = 1.12; 95% CI, 1.04-1.2).
A one-unit increase in O3 was associated with a 3% lower chance of having extremely dense breasts and a 2% higher changes of having fatty breasts.
Researchers found no clinically relevant differences in variables such as menopausal status or the use of hormone replacement therapy.
“Our findings suggest that previously reported geographic variation in breast density could, in part, be explained by different air pollution patterns in urban and rural areas,” Yaghjyan said. “Breast density is a well-established and strong breast cancer risk factor, so future studies are warranted to determine if the observed associations are causal which, if confirmed, may have implications for risk prevention.” – by Chuck Gormley
Disclosure: The NCI funded this study. The researchers report no relevant financial disclosures.