A new National Institutes of Health analysis has found an association between higher blood levels of two legacy PFAS chemicals and estrogen receptor-negative breast cancer. The result is important because ER-negative tumors tend to have fewer known risk factors and can be harder to treat, but it does not show that PFAS exposure caused cancer in any individual woman.
The study, published in the Journal of Clinical Oncology, examined perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS) and 15 other per- and polyfluoroalkyl substances. Researchers measured the chemicals in blood collected before participants were diagnosed with breast cancer, which strengthens the timing of the analysis compared with measurements taken after a diagnosis.
What the researchers reported
The analysis included 1,609 women who developed breast cancer and a comparison sample of 2,269 women. Participants came from the NIH Sister Study, a long-running cohort of women in the United States and Puerto Rico who did not have breast cancer when they enrolled but had a full or half-sister who had previously been diagnosed.
Women in the group with the highest PFOA concentrations had a 67% higher rate of ER-negative breast cancer than women in the lowest group. For PFOS, the rate was 93% higher. Those figures are relative comparisons between groups. They are not the same as saying that an individual woman’s absolute chance of developing breast cancer increased by 67% or 93%.
The researchers did not find a clear association between PFOA or PFOS and breast cancer overall. The signal was concentrated in ER-negative disease, a subtype whose cells do not carry estrogen receptors. That distinction matters because breast cancer is not one condition with a single set of causes.
Association is not proof of causation
This was an observational study. It can identify patterns between measured exposure and later health outcomes, but it cannot by itself prove that a chemical caused a tumor. Other exposures, biological differences or unmeasured factors may contribute to the result. The investigators also noted that proposed pathways involving gene activity or the immune system were not directly tested in this analysis.
The Sister Study is a valuable research cohort, yet its participants are not a random sample of the general population: every enrollee had a sister with breast cancer. That family-history design helps scientists study risk, but it also means the percentages should not be used as a personal risk calculator.
Why PFOA and PFOS still matter
PFAS are a large family of synthetic chemicals used in products such as water-resistant materials, some food packaging and firefighting foams. Their strong chemical bonds allow many of them to persist in the environment and in the body, which is why they are often called “forever chemicals.”
PFOA and PFOS have been largely phased out in the United States, but past use and environmental persistence mean that measurable exposure remains common. Newer replacement PFAS require separate study; the new analysis should not be assumed to describe every chemical in this broad class.
What this result does—and does not—change
The findings add to evidence that environmental exposures may influence specific breast cancer subtypes. They also support further research in populations with higher PFAS exposure and in groups more affected by ER-negative disease.
They do not create a new screening test or a reason to change breast cancer treatment. People concerned about exposure can consult local water-quality information and public-health guidance, especially in communities with known contamination. Medical screening decisions should still be based on established guidance and an individual discussion with a qualified clinician.
Future work will need to test the result in additional populations, examine newer PFAS and clarify whether reducing exposure changes disease risk. Until then, the most accurate reading is cautious: two legacy PFAS were associated with ER-negative breast cancer in this analysis, while overall breast cancer risk did not show a clear link.
Primary sources: NIH news release and study summary; Chang CJ, Pullella K, Keil AP, et al., Per- and Polyfluoroalkyl Substance Exposure and Breast Cancer Incidence in the Sister Study, Journal of Clinical Oncology.
Image: Julia Koblitz / Unsplash, used under the Unsplash License. Source page. The photograph is illustrative and does not depict study participants.
