Women with the highest levels of a chemical called PFOS had a 93% higher rate of ER-negative breast cancer than women with the lowest levels. That’s according to a National Institutes of Health analysis published in the Journal of Clinical Oncology in November 2026. The blood samples were taken years before anyone was diagnosed, which makes the link stronger. The chemicals, PFOA and PFOS, are man-made. They are found in nonstick pans, food packaging, and outdoor clothing. Most Americans have some in their bodies.
The study does not show that PFOA or PFOS raise breast cancer risk in general. The higher risk showed up only in estrogen receptor-negative (ER-negative) tumors. This type of breast cancer is more aggressive and harder to treat than ER-positive cancer.
What are PFAS, and why are they so common?
PFAS stands for per- and polyfluoroalkyl substances. It’s a family of thousands of man-made chemicals. They are held together by a very strong bond between carbon and fluorine atoms. That bond makes them useful in industry. It also means they don’t break down in nature or in the body, which is why they’re called “forever chemicals.” According to the Washington State Department of Health, common sources include nonstick pans, food wrappers and packaging, and outdoor clothing. Because they repel water, grease, and stains, they were used widely for most of the late 1900s.
The NIH Study: Design, Scale, and Key Findings
The study is a large look at PFAS and breast cancer risk. It used data from a long-running federal study called the Sister Study. It is led by NIH’s National Institute of Environmental Health Sciences and looks at how environment and genes affect breast cancer risk. None of the women had breast cancer when they joined. But each had a sister or half-sister who had been diagnosed with it.
NIH researchers measured 17 types of PFAS in blood taken before anyone was diagnosed with cancer. The analysis included 1,609 women who later got breast cancer and 2,269 women for comparison. The team looked at each PFAS and each tumor type. Only PFOA and PFOS were linked to ER-negative breast cancer. The other PFAS showed no higher risk, and there was no higher risk for breast cancer overall.
Read More: Georgia’s Forever Chemical Cover-Up: What We Now Know
The links were large. Women with the highest PFOA levels had a 67% higher rate of ER-negative breast cancer than women with the lowest levels. For PFOS, the rate was 93% higher. These numbers compare groups. They don’t tell any one woman her actual chance of getting breast cancer.
Neither chemical was clearly linked to breast cancer overall. The fact that the risk showed up only in ER-negative tumors may hint at how these chemicals affect breast tissue.
Why does the ER-negative finding matter?
Breast cancer is not just one disease. Doctors sort tumors partly by whether they have receptors for estrogen. Estrogen is a hormone that helps some cancer cells grow. ER-positive cancers can often be treated with hormone drugs that block estrogen. ER-negative tumors don’t have these receptors, so those drugs don’t work.
ER-negative breast cancer usually grows faster and has a worse outlook than ER-positive cancer. There are fewer treatment options, so results tend to be worse. Scientists also know less about what raises the risk of this type. Most known breast cancer risk factors, like past use of hormone birth control and some lifestyle habits, are more tied to ER-positive tumors. The NIH findings may point to a risk for ER-negative cancer that people can lower.
How PFAS May Interfere With Cancer Biology
The study suggested a few ways PFAS might raise the risk of ER-negative breast cancer. PFAS may disrupt hormones and throw off the body’s normal hormone signals. They may damage DNA or weaken the cell’s ability to repair it. Or they may weaken the immune system, which normally kills abnormal cells before they become tumors. The study only observed people, so it can’t confirm which of these, if any, is the cause.
Because the study observed people, it shows a strong link but does not prove cause and effect. The link held up in a large group of women and was backed by a review of past studies.
A Meta-Analysis That Corroborates the Core Finding
Alexandra White, Ph.D., is an NIH Stadtman Investigator and the study’s lead author. Her team checked the Sister Study results against past research. “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,” White said.
The authors say future studies should look at people with higher PFAS exposure. They should also look at groups more affected by ER-negative breast cancer. And they should study the newer PFAS chemicals that replaced the old ones, since little is known about their health effects.
The Replacement PFAS Problem
PFOA and PFOS can still be found in people’s bodies and in the environment. “More research is needed, particularly evaluating the risk of breast cancer associated with newer replacement PFAS chemicals,” White said.
The newer chemicals tend to be smaller molecules. They may not stay in the body as long as the older ones. But the study notes that their health effects are still mostly unknown. White said the newer chemicals “tend to be shorter-chain compounds and may be less persistent in our bodies and the environment, but we know little about how they may influence health outcomes, such as breast cancer.”
The Broader Cancer Picture for PFAS
This NIH study adds to growing research linking PFAS to cancer. The first author is Che-Jung Chang, Ph.D. She is a former NIH research fellow who now works at DLH, a science research company. She noted that even though PFAS last a long time in nature and in the body, exposure is “potentially modifiable.” That means changing some habits can cut how much PFAS gets into your body over time.
The 1,609 women who got breast cancer had their blood taken years before diagnosis. Their chemical levels back then were already linked to higher rates of ER-negative cancer. Until now, this type of cancer had no known trigger in the environment.
What to Do Now
We know how PFAS get into the body, and there are simple ways to cut your exposure. For most Americans, drinking water is the main source. A certified water filter can lower PFAS in your water. Look for granular activated carbon or reverse osmosis filters. Not every filter removes PFAS, so check that it’s certified for PFAS removal. If you use well water, get it tested. Private wells aren’t covered by the testing rules for public water systems.
Cookware is the second big area. Most nonstick pans use PFAS. Cooking on lower heat may limit how much chemical is released. Using wooden utensils instead of metal ones on nonstick pans avoids scratches that can raise exposure. When you replace pans, cast iron, stainless steel, and glass are easy PFAS-free choices.
Check other products too. Labels that say “waterproof,” “stain-resistant,” or “grease-proof” can mean PFAS are in clothing, fabrics, food packaging, or personal care products. Grease-resistant takeout boxes and microwave popcorn bags are other common sources to cut back on.
None of these steps will remove PFAS from your life completely. The chemicals are too widespread for that right now. But the Sister Study adds weight to the idea that lowering your own exposure matters. This is especially true for women at higher risk of ER-negative breast cancer, including those with a family history of the disease.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.