Women with higher blood levels of two common per- and polyfluoroalkyl substances face a higher estimated rate of developing an aggressive form of breast cancer, according to a new study by the National Institutes of Health released on November 5, 2026.
Often referred to as forever chemicals,
these synthetic compounds resist environmental breakdown and accumulate in human tissue over years. The research focuses on perfluorooctanoic acid, known as PFOA, and perfluorooctanesulfonic acid, known as PFOS.
Investigators analyzed blood plasma collected years before cancer diagnoses from participants in the Sister Study, a project led by the National Institute of Environmental Health Sciences. The larger study enrolled 50,884 women ages 35–74 in the United States and Puerto Rico from 2003 to 2009.
None of the participants had breast cancer when they joined, though each had a full or half-sister with a previous breast cancer diagnosis. For their specific PFAS analysis, researchers included 1,609 women who developed breast cancer and a comparison sample of 2,269 women, with the groups overlapping by 114 women.
To improve statistical power, investigators oversampled estrogen receptor-negative cases, including 324 ER-negative and 1,120 ER-positive tumors. Women in the group with the highest PFOA levels showed a 67% higher estimated rate of estrogen receptor-negative breast cancer than those in the lowest group. For PFOS, the rate was 93% higher.
These figures reflect relative differences between groups rather than an individual woman’s overall chance of developing the disease. The study found no clear association between either chemical and breast cancer overall, or between those chemicals and estrogen receptor-positive tumors.
Our findings, which we confirmed using a meta-analysis of prior research, indicate that certain legacy PFAS, including PFOA and PFOS, are associated with a higher risk of ER-negative breast cancer, a more aggressive tumor type with few known risk factors,
Alexandra White, Ph.D., NIH Stadtman Investigator
ER-negative tumors lack the cellular receptors that allow the hormone estrogen to drive cancer growth. These tumors typically prove more aggressive than hormone-responsive cancers, leaving medical researchers with fewer established risk factors to study.
Federal health officials emphasized the need for continued scrutiny of environmental exposures. Women deserve clear answers about how chemicals in their environment may affect their health,
said HHS Secretary Robert F. Kennedy, Jr., in a statement reported by the National Institutes of Health.
This NIH study links two forever chemicals to a higher risk of ER-negative breast cancer and demands further investigation. Under President Trump’s leadership, we will pursue the evidence, confront environmental health risks, and give women the information they need to protect their health.
Robert F. Kennedy, Jr., HHS Secretary
Although major manufacturers have largely phased out older legacy compounds like PFOA and PFOS, measurable levels remain present in most individuals. Researchers note that exposure pathways warrant further examination alongside newer replacement compounds introduced by industry.
Although PFAS are persistent in the environment and in our bodies, exposure to them is still potentially modifiable, meaning people can take steps to reduce their exposure, and these findings could open new avenues for prevention.
Alexandra White, Ph.D., NIH Stadtman Investigator
The findings were published in the Journal of Clinical Oncology under the title Per- and Polyfluoroalkyl Substance Exposure and Breast Cancer Incidence in the Sister Study
.