Older PFAS Chemicals Linked to ER-Negative Breast Cancer
A NIH cohort study found higher blood levels of PFOA and PFOS were tied to ER-negative breast cancer, though not overall breast cancer risk.
Updated on Nov. 5, 2026 in Cancer
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A National Institutes of Health study found that women with higher blood levels of PFOA and PFOS, two long-used PFAS chemicals, had higher rates of estrogen receptor-negative (ER-negative) breast cancer, while no clear link appeared with overall breast cancer risk. The findings are relevant to women in the United States and Puerto Rico who may have been exposed to these compounds in the past.
Why it matters
ER-negative breast cancer is a subtype that does not respond to standard hormone-blocking therapies, so identifying possible environmental contributors matters for prevention and research priorities. The study suggests PFAS exposure may affect cancer risk through pathways that are not hormonal, which could shift how researchers think about these chemicals. PFOA and PFOS have been largely phased out, but their long persistence in the body and the environment keeps the question relevant.
This prospective cohort analysis drew on the Sister Study, which enrolled 50,884 women ages 35-74 from 2003 to 2009, and measured 17 PFAS compounds in blood collected years before diagnosis. The findings were reported in the Journal of Clinical Oncology and confirmed with a meta-analysis of prior research.
The players
National Institutes of Health
The NIH is the primary federal agency for biomedical and health research, supporting a wide range of cancer and environmental health studies.
Journal of Clinical Oncology
The Journal of Clinical Oncology is a peer-reviewed publication covering clinical research on cancer diagnosis, treatment and prevention.
The details
Researchers measured PFAS levels in blood plasma collected years before cancer diagnoses and compared breast cancer incidence across groups defined by those levels. The authors suggest PFAS may influence cancer risk through non-hormonal biologic pathways, which would help explain why the association appeared for ER-negative tumors specifically. Because the measurements came before diagnosis, the design supports a temporal sequence, though it cannot by itself prove cause and effect.
Timeline
Sister Study enrolled 50,884 women between 2003 and 2009.
NIH published the study findings on November 5, 2026.
Health Landscape
The findings add to a growing body of research on PFAS and cancer, extending earlier Sister Study analyses to a specific chemical class. Breast cancer subtype research is shifting toward environmental exposures that may affect tumors not driven by estrogen, a gap in prevention knowledge.
Women who have a history of higher environmental exposure to PFAS may find it worth raising this research with their doctor during routine breast health discussions. The strongest population-level signal concerns ER-negative breast cancer, so people with family history questions should keep that subtype in mind.
The takeaway
The key insight is that PFAS exposure measured in blood before diagnosis was tied to higher ER-negative breast cancer rates, not overall breast cancer risk. Talk with your physician about any personal concerns related to chemical exposure and breast health.
Further reading
For more on how environmental exposures are studied alongside Cancer research, explore our coverage of the disease.
Source note: This article includes information reported by National Institutes of Health (NIH).
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