Updated

An NIH study published November 12, 2026 in the Journal of Clinical Oncology found that women with higher blood levels of two common forever chemicals, PFOA and PFOS, had higher rates of an aggressive breast cancer type. Women in the highest PFOA group had a 67% higher rate of ER-negative breast cancer than those in the lowest group, and the highest PFOS group had a 93% higher rate. The study was led by NIH Stadtman Investigator Alexandra White, with first author Che-Jung Chang, and drew on blood samples from the Sister Study, which enrolled 50,884 U.S. and Puerto Rican women ages 35 to 74 between 2003 and 2009. The analysis covered 1,609 women who later developed breast cancer and 2,269 comparison women. The researchers stressed that the findings show an association, not proof that the chemicals cause the disease, and that the percentages are relative differences rather than individual risks. No clear link between either chemical and overall breast cancer risk was found. ER-negative tumors lack estrogen receptors and generally have poorer outcomes, and little is known about their causes. The study did not test mechanisms such as gene activity or immune changes, which remain uncertain. Chang said PFAS exposure may be modifiable, and the researchers called for further work in more exposed and higher-risk populations.