A new federal study connects higher blood levels of two common “forever chemicals” with increased rates of an aggressive breast cancer subtype, adding evidence to a growing debate over PFAS exposure, drinking-water safety, and corporate liability.
Researchers found that women in the highest exposure group had a 67% higher estimated rate of estrogen receptor-negative breast cancer for PFOA and a 93% higher rate for PFOS compared with women in the lowest exposure groups, according to the National Institutes of Health’s November 5 announcement. The figures reflect relative differences in adjusted rates, not an individual woman’s chance of developing cancer.
The results appeared two days after 3M announced a $7.35 billion agreement concerning PFAS-related personal-injury claims. The Dallas Express examined the settlement and the separate questions it leaves about firefighters’ protective equipment. The company outlined the nominal payment schedule and participation conditions in a November 3 SEC filing.
What The Full Study Shows
The researchers measured 17 PFAS chemicals in blood collected before cancer diagnoses.
The analysis drew from the NIH Sister Study, which enrolled 50,884 women in the United States and Puerto Rico between 2003 and 2009. Each participant had a full or half-sister with breast cancer but did not have the disease at enrollment.
Their case-cohort analysis included 1,609 breast cancer cases and 2,269 participants in a comparison sample; the groups overlapped by 114 women. Investigators oversampled estrogen receptor-negative tumors to strengthen that analysis, including 324 ER-negative and 1,120 ER-positive cases with those classifications.
Estrogen receptor-negative cancers do not have receptors through which estrogen drives tumor growth. Such tumors tend to have poorer outcomes than estrogen receptor-positive cancers. The researchers found no clear association between PFOA or PFOS and breast cancer overall, or between those chemicals and estrogen receptor-positive tumors.
The investigators also combined the new data with earlier studies that measured PFAS before cancer diagnosis. That meta-analysis found a statistically supported association for PFOA and estrogen receptor-negative cancer, with a pooled relative risk of 1.30. The pooled PFOS estimate reached 1.20, but its 95% confidence interval of 0.91 to 1.58 included no increased risk, leaving that combined result uncertain.
The researchers adjusted their models for factors including age, reproductive history, body mass index, smoking, alcohol use, and other PFAS exposures. Still, their observational design cannot establish that PFAS caused the tumors. Because the Sister Study recruited women with a family history of breast cancer, the findings may not apply equally to all women.
Texas Exposure And Firefighter Questions
The Dallas Express has extensively examined PFAS in Texas water systems and covered Texas State University research involving firefighter equipment and contaminated wash water. Earlier this year, the newsroom also investigated the Pentagon’s position on PFAS in protective firefighting gear.
3M’s latest settlement identifies six covered medical conditions, including certain cancers, but does not list breast cancer. The company does not admit liability. Texas also sued 3M and DuPont-related businesses in 2024 over alleged misleading marketing of PFAS-containing consumer products.
What Consumers Can Do
PFOA and PFOS persist in the environment even after their widespread phaseout.
The Environmental Protection Agency sets federal drinking-water limits of 4 parts per trillion for each chemical. Residents can check their water provider’s testing information and consider independently certified filtration systems designed to reduce PFAS.
In May, the EPA proposed letting eligible water systems request an extension until 2031; that proposal does not change the current 4-parts-per-trillion limits.
The researchers urged further studies of highly exposed populations and newer replacement chemicals. They did not establish that using any particular filter prevents breast cancer.
