Women with the highest blood levels of two long-used “forever chemicals” were more likely to develop an aggressive form of breast cancer, according to a National Institutes of Health analysis that is drawing wide attention this week. The study, published in the Journal of Clinical Oncology, linked the chemicals PFOA and PFOS to estrogen receptor-negative (ER-negative) breast cancer, but found no clear link to breast cancer overall.
The researchers stress that the results show an association, not proof that the chemicals cause cancer. Still, the findings add to growing scientific concern about PFAS, a large family of chemicals that break down very slowly and can stay in the body for years.
What the study found
The team used data from the Sister Study, a long-running project led by the National Institute of Environmental Health Sciences. It enrolled 50,884 women ages 35 to 74 in the U.S. and Puerto Rico between 2003 and 2009. Every participant had a sister who had been diagnosed with breast cancer, but none had the disease herself when she joined.
Researchers measured 17 different PFAS in blood samples collected years before any diagnosis. They compared 1,609 women who later developed breast cancer with 2,269 women in a comparison group. According to the HHS announcement and The ASCO Post:
- Women in the highest PFOA group had a 67% higher rate of ER-negative breast cancer than those in the lowest group.
- For PFOS, the highest group had a 93% higher rate than the lowest.
- No similar link was seen for ER-positive tumors.
- A few other PFAS showed weak or uncertain signals that need more study.
Those percentages compare groups of women. They are not the chance that any one woman will get cancer. The researchers also pooled earlier studies in a separate review, which supported the PFOA finding and pointed the same direction, less conclusively, for PFOS, The ASCO Post reported.
Why ER-negative breast cancer matters
ER-negative tumors lack the estrogen receptors that many breast cancers rely on to grow. According to the HHS release, they tend to be more aggressive, have worse outcomes, and their risk factors are less well understood than those of other breast cancers. That makes any clue about what raises the risk especially valuable to scientists.
Lead author Alexandra White of NIH said the work “provides evidence that two PFAS are related to a higher ER-negative breast cancer risk,” Fox News reported. She also described PFAS exposure as “potentially modifiable,” according to HHS, meaning it is something people and communities may be able to reduce, unlike age or family history.
Important limits
Because every woman in the study had a sister with breast cancer, the results may not apply to all women. Some subgroups were small, and the study did not test how the chemicals might affect breast tissue. The authors suggested possible non-hormonal pathways, such as changes in how genes are switched on or effects on the immune system, but those ideas still need testing, The ASCO Post noted.
There is also a timing question. PFOA and PFOS have largely been phased out and replaced by newer PFAS. Most people still carry measurable amounts of the older chemicals, but far less is known about the replacements. The researchers said the newer compounds’ cancer risk needs more study.
Legal and financial pressure over PFAS has been building too. Upstormed News has reported that 3M agreed to a $7.35 billion deal over PFAS firefighting foam injury claims.
Why it matters for families
PFAS have been used for decades in common consumer products, which is why nearly everyone has some in their blood. This study does not mean anyone should panic, and it does not give individuals a way to measure their own risk. It does give families one more reason to pay attention to environmental exposures at home, much like testing for radon or checking local water quality reports.
If you have a family history of breast cancer, or questions about breast cancer screening or chemical exposures, talk with your doctor. They can help you understand your personal risk and which screenings make sense for you. This article is for general information only and is not medical advice.
What to watch next
The researchers called for studies of people with higher exposures and of the newer replacement chemicals. Watch for follow-up research and for how regulators respond as evidence builds. Upstormed News will follow this story.
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Sources: HHS/NIH, “Two ‘forever chemicals’ associated with higher risk of aggressive breast cancer in NIH analysis” (November 5, 2026); The ASCO Post, “Two ‘Forever Chemicals’ Associated With Higher Risk of ER-Negative Breast Cancer” (November 9, 2026); Fox News, “Aggressive cancer type linked to common chemical exposure in new study” (November 10, 2026); Journal of Clinical Oncology, “Per- and Polyfluoroalkyl Substance Exposure and Breast Cancer Incidence in the Sister Study” (2026)
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