Study Finds High Levels of PFAS Chemicals Associated with Breast Cancer

ER-negative breast cancer rates were higher in people with higher levels of two PFAS forever chemicals in their blood.

Nov. 6, 2026

Key Highlights

Higher blood levels of PFOA and PFOS were associated with increased rates of ER-negative breast cancer.
The highest PFOA group had a 67% higher rate, and the highest PFOS group had a 93% higher rate, than the respective lowest groups.
Researchers found no clear association between these chemicals and breast cancer risk overall.
The study measured 17 PFAS in blood collected years before participants were diagnosed.
Researchers say PFAS may affect risk through non-hormonal pathways, but further studies are needed.

A new study by the NIH found that women with higher blood levels of two PFAS “forever chemicals” were more likely to develop estrogen receptor-negative (ER-negative) breast cancer.

Women with higher blood plasma levels of two of these substances – PFOA and PFOS – were associated with higher incidences of ER-negative breast cancer. No clear association was observed between the two chemicals and breast cancer risk overall.

ER-negative tumors lack receptors that allow hormone estrogen to help cancer cells grow. They tend to be more aggressive and have worse outcomes.

NIH researchers measured 17 PFAS in blood, collected years before the patients were diagnosed with cancer. Women with the highest PFOA levels had a 67% higher rate of ER-negative breast cancer than those in the lowest group; for PFOS, the rate was 93% higher. This built on a different study led by the NIH’s National Institute of Environmental Health Sciences (NIEHS).

The authors suggest that PFAS may affect cancer risk through other non-hormonal biologic pathways. Possibly pathways include changes in gene activity or the immune system. Future studies should evaluate people with higher PFAS exposure and in groups more affected by ER-negative breast cancer, the authors say.