The study suggests that higher exposure to per- and polyfluoroalkyl substances (PFAS), specifically perfluorooctanesulfonic acid (n-PFOS), may increase a person’s risk for thyroid cancer by 56%.
Several news outlets played up the findings, published online in eBioMedicine. “Dangerous ‘Forever Chemicals’ in Your Everyday Items Are Causing Cancer,” Newsweek reported.
But Gideon Meyerowitz-Katz, PhD, an epidemiologist at the University of Wollongong (Australia), voiced his skepticism.
“While it’s possible that PFAS might be causing thyroid cancer, the evidence thus far is unconvincing and probably not worth worrying about,” said Dr. Meyerowitz-Katz, who was not involved in the research.
PFAS and thyroid cancer
PFAS are a class of widely used synthetic chemicals found in many consumer and industrial products, including nonstick cookware, stain-repellent carpets, waterproof rain gear, microwave popcorn bags, and firefighting foam.
These substances have been dubbed “forever chemicals” because they do not degrade and are ubiquitous in the environment.
Exposure to endocrine-disrupting chemicals, including PFAS, has been identified as a potential risk factor for thyroid cancer, with some research linking PFAS exposure to thyroid dysfunction and carcinogenesis.
To investigate further, the researchers performed a nested case-control study of 86 patients with thyroid cancer using plasma samples collected at or before diagnosis and 86 controls without cancer who were matched on age, sex, race/ethnicity, body weight, smoking status, and year of sample collection.
Eighteen individual PFAS were measured in plasma samples; 10 were undetectable and were therefore excluded from the analysis. Of the remaining eight PFAS, only one showed a statistically significant correlation with thyroid cancer.
Specifically, the researchers found that exposure to n-PFOS was associated with a 56% increased risk for thyroid cancer among people who had a high level of the chemical in their blood (adjusted odds ratio, 1.56; P = .004). The results were similar when patients with papillary thyroid cancer only were included (aOR, 1.56; P = .009).
A separate longitudinal analysis of 31 patients diagnosed with thyroid cancer 1 year or more after plasma sample collection and 31 controls confirmed the positive association between n-PFOS and thyroid cancer (aOR, 2.67; P < .001). The longitudinal analysis also suggested correlations for a few other PFAS.
“This study supports the hypothesis that PFAS exposure may be associated with increased risk of thyroid cancer,” the authors concluded.
But in a Substack post, Dr. Meyerowitz-Katz said that it’s important to put the findings into “proper context before getting terrified about this all-new cancer risk.”
First, this study was “genuinely tiny,” with data on just 88 people with thyroid cancer and 88 controls, a limitation the researchers also acknowledged.
“That’s really not enough to do any sort of robust epidemiological analysis – you can generate interesting correlations, but what those correlations mean is anyone’s guess,” Dr. Meyerowitz-Katz said.
Even more importantly, one could easily argue that the results of this study show that most PFAS aren’t associated with thyroid cancer, given that there was no strong association for seven of the eight PFAS measured, he explained.
“There are no serious methodological concerns here, but equally there’s just not much you can reasonably gather from finding a single correlation among a vast ocean of possibilities,” Dr. Meyerowitz-Katz wrote. “Maybe there’s a correlation there, but you’d need to investigate this in much bigger samples, with more controls, and better data, to understand what that correlation means.”
Bottom line, Dr. Meyerowitz-Katz explained, is that “the link between PFAS and thyroid cancer is, at best, incredibly weak.”
Funding for the study was provided by the National Institutes of Health and The Andrea and Charles Bronfman Philanthropies. One coauthor is cofounder of Linus Biotechnology and is owner of a license agreement with NIES (Japan); received honoraria and travel compensation for lectures for the Bio-Echo and Brin foundations; and has 22 patents at various stages. Dr. Meyerowitz-Katz has no relevant disclosures.
A version of this article appeared on Medscape.com.