TL;DR
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A prospective study linked higher measured levels of PFOA and PFOS with greater risk of estrogen receptor-negative breast cancer, a subtype that is generally more aggressive. The findings are observational and do not establish that the chemicals caused the cancers; a review of seven studies also found an association for PFOA, but not a statistically clear one for PFOS.
A prospective study found that women with the highest measured blood levels of PFOA and PFOS had higher rates of estrogen receptor-negative breast cancer than women with the lowest levels, researchers reported November 5. The findings indicate an association, not proof that exposure caused the cancers, but matter because this subtype is generally more aggressive and has fewer established risk factors.
Researchers led by Alexandra J. White, PhD, of the National Institute of Environmental Health Sciences, analyzed data from the U.S. Sister Study. Among women in the highest exposure group, the estimated risk of ER-negative breast cancer was higher than in the lowest group for PFOA (hazard ratio 1.67, 95% confidence interval 1.10–2.53) and PFOS (hazard ratio 1.93, 95% CI 1.15–3.22). These estimates compare exposure quartiles; they do not show an individual woman’s chance of developing cancer.
The cohort included women ages 35 to 74 who had a sister diagnosed with breast cancer and had not themselves been diagnosed when they enrolled. For the analysis, the team included 1,609 women who developed breast cancer and a comparison sample of 2,269 women. Participants were followed for median periods of 5.9 and 9.7 years, respectively. Researchers measured 17 PFAS in blood plasma collected before diagnosis, and oversampled women with ER-negative tumors because those cancers are less common and harder to study.
A meta-analysis of seven studies also found an association between PFOA and ER-negative breast cancer (relative risk 1.30, 95% CI 1.05–1.62). For PFOS, the estimate was 1.20, but its confidence interval included no association (95% CI 0.91–1.58). The study appeared in the Journal of Clinical Oncology, according to the report.
Why ER-Negative Findings Matter
The results add evidence about possible environmental contributors to ER-negative breast cancer, which is generally more aggressive and has fewer known risk factors than some other breast cancer subtypes. The researchers said the concentration of positive findings among hormone receptor-negative tumors may point to mechanisms other than conventional hormone disruption, including possible epigenetic changes or immune effects. Those mechanisms remain explanations under consideration, not findings established by this study.
PFAS are a large family of persistent chemicals, and the compounds measured here have been phased out of industrial use and largely replaced by other PFAS, White told MedPage Today. The findings are still relevant because people may retain measurable levels of older compounds, while health effects of newer replacements remain a concern for research. The study does not quantify the risk posed by any particular source or show that reducing exposure prevents cancer.
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How Researchers Measured Exposure
The Sister Study enrolled 50,884 breast-cancer-free women in the United States and Puerto Rico from 2003 to 2009. Each participant had a full or half-sister with breast cancer. The researchers used blood samples collected before diagnosis to measure chemical concentrations, which helps establish that the measured exposure preceded the cancers recorded during follow-up. It does not, by itself, establish that exposure was the cause.
The analysis also reported other findings, underscoring that results differed by chemical and tumor type. A possible association between n-methylperfluoro-1-octanesulfonamidoacetic acid and ER-negative tumors did not reach statistical significance. Perfluoro-n-tridecanoic acid was inversely associated with those tumors, while PFOSA was associated with ER-positive tumors but was detected in only 6.9% of participants. For overall breast cancer incidence, most PFAS showed negligible associations; several estimates were described as suggestive rather than conclusive.
“Our positive findings were generally concentrated among hormone receptor-negative tumors.”
— Alexandra J. White and colleagues, in the study
Limits of the Evidence
This was an observational study, so it can identify patterns but cannot establish that PFOA or PFOS caused breast cancer. The supplied report does not specify the women’s individual exposure sources, and the results do not show whether changing exposure would alter a person’s risk. The cohort was also limited to women with a sister who had breast cancer, so the findings may not apply equally to all populations.
The findings for individual chemicals were not uniform, and some estimates had confidence intervals that included no association. Although the meta-analysis supports an association for PFOA, the PFOS estimate was less conclusive. Further research is needed to test the results in other populations, clarify possible biological pathways, and examine replacement PFAS.
Research on PFAS Replacements
The researchers called for more attention to the health effects of replacement PFAS now in wider use, alongside further study of established compounds and breast cancer subtypes. Replication in other cohorts and investigation of exposure sources could help determine how broadly the observed associations apply and whether particular chemicals or pathways are involved.
White told MedPage Today that reducing exposure from sources such as contaminated water could be a reasonable step for people concerned about PFAS. The study did not test exposure-reduction measures or show that they prevent cancer. It remains unclear what specific next study or public health action will follow from this report.
Key Questions
What did the study find?
Women in the highest measured exposure quartile for PFOA and PFOS had higher estimated risks of ER-negative breast cancer than women in the lowest quartile. The study found an association, not proof that the chemicals caused the cancers.
What are PFOA and PFOS?
PFOA and PFOS are types of PFAS, a broad group of persistent chemicals. The report says the two compounds assessed have been phased out from industry and largely replaced by other PFAS.
Does this mean PFAS cause breast cancer?
No. The research was observational and cannot establish cause and effect. The findings point to an association that requires further investigation.
Did the study find a link with all breast cancers?
The strongest reported associations concerned ER-negative tumors. For overall breast cancer incidence, researchers reported negligible associations for most PFAS, with a few estimates described as suggestive.
What should people concerned about exposure know?
White told MedPage Today that reducing exposure from sources such as contaminated water could be reasonable for people concerned about PFAS. This study did not test whether exposure reduction lowers cancer risk; questions about specific exposure should be discussed with relevant public health or environmental authorities.
Source: medpagetoday.com
