Forever Chemicals and Aggressive Breast Cancer: The Facts

If you live in the United States, there is almost certainly a little PFOA and PFOS in your blood right now. These are two "forever chemicals," part of a big family called PFAS. They were used for decades to make things resist stains and water. The federal health agency ATSDR says nearly all people in the U.S. have PFAS in their blood.

So when a post from @hashem.alghaili spread on Instagram around November 8, 2026, it hit a nerve. It said: "Women with high blood levels of a forever chemical had a 93% higher rate of aggressive breast cancer, an NIH analysis found." The study behind it is real, and the post mostly gets it right. But the 93% means something different from what many readers will assume. Here is what the scientists actually found.

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Blood saved years before any cancer

The study comes from the Sister Study, a long-running project at the National Institute of Environmental Health Sciences (NIEHS), part of NIH. Between 2003 and 2009, it signed up 50,884 women ages 35 to 74 in the United States and Puerto Rico. Each had a sister or half-sister who had breast cancer. None had breast cancer herself when she joined. Each woman gave a blood sample at the start.

That stored blood is what makes this study useful. Measuring a chemical after someone is already sick makes it hard to know which came first. Here, the blood was taken years before any diagnosis.

The team, led by Che-Jung Chang and Alexandra White of NIEHS, measured 17 different PFAS in those samples. They looked at 1,609 women who later got breast cancer. They compared them with a group of 2,269 women drawn from the whole study. The paper was published on November 5, 2026, in the Journal of Clinical Oncology.

The finding was about one kind of breast cancer

Breast cancers are sorted partly by whether the cells have receptors (docking spots) for the hormone estrogen. Most are ER-positive, meaning estrogen can help them grow. A smaller group is ER-negative. NIH says ER-negative cancers "tend to be more aggressive and have worse outcomes," and that less is known about what causes them. That is why the post called it "aggressive." For more, see what hormone receptor status means.

The researchers made sure to include plenty of ER-negative cases so they could study them well: 324 women in the study had ER-negative breast cancer and 1,120 had ER-positive.

When they looked at breast cancer as a whole, they found no clear link with PFOA or PFOS. The link showed up only for ER-negative cancer. The researchers split the women into four equal groups by blood level. Compared with the lowest group, women in the highest group had:

• a 67% higher rate of ER-negative breast cancer for PFOA
• a 93% higher rate, nearly double, for PFOS

A third chemical, N-MeFOSAA, pointed the same way but less clearly. One more, PFTrDA, went the other way: higher levels went with a lower rate of ER-negative cancer. That does not mean it protects anyone. It is a reminder that a single study can turn up odd results, and that findings need to be repeated.

What "93% higher" really means

Here is the part a short post cannot hold. A 93% higher rate compares two groups of women. It does not mean a 93% chance of anything.

Susan Neuhausen, a cancer researcher at City of Hope who was not part of the study, walked through the math for the news site Healio. About 13% of women, or one in eight, get breast cancer in their lifetime. About 20% to 30% of those cancers are ER-negative. So the average woman's lifetime chance of ER-negative breast cancer is about 3%. For women in the highest PFOA group, she estimated it at about 5.1%.

In other words, a jump that sounds huge as a percentage works out to about two extra cases for every 100 women over a lifetime. That is real and worth taking seriously, but it is not the same as a near-certain danger. Alexandra White, the study's senior author, said the same thing in plainer words: "these are relative hazards. On an absolute scale, the risk contributed here is going to be lower." Our guide to reading cancer statistics in the news explains this trap in more detail.

Did it hold up with other studies?

The post says the result "held up when pooled with earlier research." That is partly true.

The authors also ran a combined analysis, called a meta-analysis, of seven studies that measured PFAS in blood before diagnosis. For PFOA, the combined result still pointed to a higher risk of ER-negative breast cancer, about 30% higher, and it was statistically clear. For PFOS, the combined result was about 20% higher, but the range of likely values included no difference at all. So the pooled evidence clearly backs PFOA. For PFOS it leans the same way but is not settled.

Notice, too, that the pooled numbers are smaller than the 67% and 93% from the Sister Study alone.

The authors' own conclusion is careful. They say PFOA and PFOS "may increase ER-negative breast cancer risk." This kind of study shows a link, not proof of cause. The team thinks PFAS might act through something other than hormones, such as the immune system or how genes are switched on. But they did not test that here.

The good news hidden in this story

PFOA and PFOS have been largely phased out in the United States. ATSDR says that from 1999-2000 to 2018-2019, the amount of PFOS in Americans' blood fell by more than 85%, and PFOA fell by more than 70%. The Sister Study blood samples were taken between 2003 and 2009, when levels were higher than they are today.

The open question is the newer PFAS that replaced them. "More research is needed, particularly evaluating the risk of breast cancer associated with newer replacement PFAS chemicals," White said in the NIH release.

The study's first author also pointed out something hopeful. Unlike family history or age, PFAS exposure is something people can change. Chang said exposure is "potentially modifiable, meaning people can take steps to reduce their exposure."

What other experts have said about PFOA and PFOS

In 2023, the International Agency for Research on Cancer (IARC) classed PFOA as "carcinogenic to humans" (Group 1) and PFOS as "possibly carcinogenic to humans" (Group 2B). For PFOA, the human evidence IARC weighed was for kidney and testicular cancer, not breast cancer. A classification rates how strong the evidence is, not how big the risk is. See how to read a carcinogen classification.

Verdict on the post

Mostly accurate. The study, the journal, the 67% and 93% figures, and the word "aggressive" all match NIH. What the post leaves out: these are comparisons between the highest and lowest groups, not one woman's chance; there was no clear link with breast cancer overall; and when pooled with earlier studies, the link was clear for PFOA but not yet for PFOS.

What you can do

You do not need to panic, and this study cannot tell any one woman her risk. But lowering your PFAS exposure is reasonable, and a few steps go a long way.

• Start with your water. EPA says people take in PFAS through drinking water, some foods, dust and soil, and some products. ATSDR says exposure from today's consumer products is "generally lower than exposures from PFAS-contaminated drinking water." Ask your water utility for its PFAS test results. If you use a private well, you would need to arrange your own testing.
• Consider a filter if your water has PFAS. EPA says home filters certified to NSF 53 or 58 standards, or reverse osmosis systems, can reduce PFAS. Our page on PFAS and cancer explains EPA's drinking-water limits and filter choices.
• Keep up with screening. Ask your doctor about breast cancer screening and your own breast cancer risk factors, such as family history.
• Know what to watch for. See a doctor about a new lump, skin or nipple changes, or nipple discharge.

Sources

• Instagram post (@hashem.alghaili): instagram.com
• Chang C-J, Pullella K, Keil AP, et al. "Per- and Polyfluoroalkyl Substance Exposure and Breast Cancer Incidence in the Sister Study." Journal of Clinical Oncology, November 5, 2026. Abstract on PubMed: pubmed.ncbi.nlm.nih.gov
• NIH news release, "Two 'forever chemicals' associated with higher risk of aggressive breast cancer in NIH analysis," November 5, 2026, as posted on EurekAlert: eurekalert.org
• Healio, "'Forever chemicals' linked to risk for aggressive breast cancer," November 6, 2026: healio.com
• ATSDR, PFAS facts and statistics: atsdr.cdc.gov
• IARC, "IARC Monographs evaluate the carcinogenicity of PFOA and PFOS," December 1, 2023: iarc.who.int
• EPA, "Our current understanding of the human health and environmental risks of PFAS": epa.gov
• ATSDR, PFAS exposure: atsdr.cdc.gov

How this article was prepared

An AI-assisted editorial system prepared this story on November 9, 2026, from the sources listed above. No named medical reviewer has reviewed it unless one is listed. Cancer Explained is published by the National Cancer Information Foundation; this is not medical advice. See an error? Tell us.