Researchers found “no clear association” between the two chemicals and breast cancer in general, according to the NIH.
Dr. Timothy Rebbeck, a professor of cancer prevention at Dana-Farber Cancer Institute and Harvard, said the findings add to growing research linking chemicals forever to some cancers, but do not establish causation.
“The data so far has really been correlation, not causation, in humans,” Rebbeck said in an interview Wednesday. “And while that is interesting and important, we still need other data that actually gives us information about causality.”
PFOA and PFOS belong to a larger group of synthetic chemicals called per- and polyfluoroalkyl substances, also known as PFAS. Used in a wide range of consumer products, these chemicals are commonly referred to as “forever chemicals” because they break down slowly and can remain in the human body for years.
The NIH researchers focused on estrogen receptor-negative breast cancer, or ER-negative breast cancer, where tumors “lack receptors that allow the hormone estrogen to help cancer cells grow,” according to the NIH statement about the new study.
Rebbeck said the findings are relevant because relatively few risk factors have been identified for ER-negative breast cancer.
“These are the types of cancers that we need to learn a lot more about,” he said. “And if everlasting chemicals play a role in that, that’s important knowledge.”
NIH researchers said that ER-negative breast cancers “tend to be more aggressive and have worse outcomes,” and that scientists “know less about what increases the risk of this type of breast cancer.”
“Our findings, which we confirmed using a meta-analysis of previous research, indicate that some existing 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,” Dr. Alexandra White, an NIH researcher who led the study, said in the release.
PFOA and PFOS, used for decades in products such as nonstick cookware, food packaging and stain-resistant clothing, have mostly been phased out. in the United States since the early 2000s but remain widespread.
Nearly all Americans have PFAS in their blood, according to the CDC, but some blood levels of PFAS, including PFOA and PFOS, have decreased. Between 1999 and 2019, blood levels of PFOS decreased by more than 85 percent and levels of PFOA by more than 70 percent, the CDC reported.
The research was based on data from the “Sister Study,” a long-term NIH study that recruited more than 50,000 women ages 35 to 74 in the United States and Puerto Rico from 2003 to 2009. Each participant had a sister who had been diagnosed with breast cancer, but none had the disease themselves when they enrolled in the study.
Researchers looked at blood samples from 1,609 women who later developed breast cancer and compared them to samples from a group of 2,269 other women. The samples were collected years before the women received their diagnoses, allowing scientists to examine whether prior exposure to PFAS was associated with their cancer risk.
The study did not determine how the chemicals might contribute to breast cancer, but researchers suggest they could affect biological processes beyond the body’s hormonal system, including changes in the immune system and gene activity.
“More research is needed, particularly to assess the breast cancer risk associated with new replacement PFAS chemicals,” White said.
Reebeck said it was too early to know whether reducing exposure to PFAS would reduce breast cancer risk, but the study authors said the findings could help find new ways to prevent certain types of breast cancer.
“Although PFAS are persistent in the environment and in our bodies, their exposure is still potentially modifiable, meaning people can take steps to reduce their exposure, and these findings could open new avenues for prevention,” White said.
Nick Stoico can be contacted at nick.stoico@globe.com.
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