A new multiyear investigation published in the American Journal of Public Health has revealed that women living in areas of the United States with poor air quality, especially those exposed to high traffic emissions, face an increased risk of developing breast cancer. The study, led by Veronica Irvin from Oregon State University’s College of Health, is one of the largest analyses to date, involving over 400,000 participants and 28,000 breast cancer cases.
Researchers integrated data from five major breast cancer cohorts, including the Nurses’ Health Studies, the Women’s Health Initiative, and the Sister Study, tracking participants for decades, even as they relocated. Using data from more than 2,600 air monitoring sites across the country, the team assessed long-term exposure to nitrogen dioxide (NO₂), fine particulate matter (PM2.5), and ozone.
Findings showed that nitrogen dioxide, a pollutant primarily produced by vehicle emissions, was linked to a 3% higher overall breast cancer risk (Hazard Ratio [HR] = 1.03; 95% Confidence Interval [CI] = 1.00–1.05). PM2.5 exposure was more strongly associated with aggressive estrogen receptor negative and progesterone receptor negative (ER/PR negative) tumors (HR = 1.14; 95% CI = 1.04–1.24) and with higher cancer rates in the Midwest (HR = 1.15; 95% CI = 1.01–1.32). Although ozone was not linked to overall breast cancer risk, it showed a modest correlation with ER/PR negative subtypes (HR = 1.10; 95% CI = 1.00–1.21).
The researchers stated that this study provides the strongest evidence yet of the association between nitrogen dioxide exposure and breast cancer risk, while also pointing to emerging links between fine particulate matter, ozone, and aggressive tumor subtypes. Supporting these findings, a large multiethnic cohort study by Wu and colleagues also reported that long-term exposure to air pollutants, especially PM2.5, is associated with an elevated risk of breast cancer.
While environmental pollution is emerging as a significant and potentially modifiable risk factor, several other established contributors are known to increase breast cancer susceptibility. These include genetic mutations such as BRCA1 and BRCA2, family history of breast or ovarian cancer, hormonal factors like early menarche, late menopause, and use of hormone replacement therapy, as well as reproductive factors such as having the first child after age 30 or never having been pregnant. Lifestyle factors including obesity, lack of physical activity, alcohol consumption, smoking, older age, and prior radiation exposure to the chest also contribute to risk.
The authors emphasized that improving air quality, particularly in densely populated urban areas with heavy traffic, may play a crucial role in reducing breast cancer risk and addressing regional health disparities. They concluded that cleaner air is not only vital for respiratory health but may also serve as an important preventive factor against cancer.
References
- White AJ, Hart JE, Quraishi SM, Bookwalter DB, Sweeney MR, Spalt EW, Hendryx MS, Irvin VL, Lane DS, Shadyab AH, Sealy-Jefferson S, Neuhouser ML, Whitsel EA, Kaufman JD, Laden F, Sandler DP. Air Pollutants and Breast Cancer Risk: A Parallel Analysis of Five Large US Prospective Cohorts. Am J Public Health. 2025 Sep 25:e1-e14.
- Wu AH, Wu J, Tseng C, Stram DO, Shariff-Marco S, Larson T, Goldberg D, Fruin S, Jiao A, Inamdar PP, Ihenacho U, Le Marchand L, Wilkens L, Haiman C, Ritz B, Cheng I. Air Pollution and Breast Cancer Incidence in the Multiethnic Cohort Study. J Clin Oncol. 2025 Jan 20;43(3):273-284.