Researchers at the US National Institutes of Health have identified an association between two widely used environmental chemicals and higher rates of an aggressive subtype of breast cancer.
The study examined per- and polyfluoroalkyl substances (PFAS), commonly known as “forever chemicals” because they break down slowly in the environment and can remain in the human body for years. The two chemicals highlighted in the findings are perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).
Editorial Insight
Key Highlights
Important points readers should notice.
The NIH study examined 17 types of PFAS in blood samples.
Higher PFOA levels were associated with a 67% higher rate of ER-negative breast cancer.
Higher PFOS levels were associated with a 93% higher rate of the same cancer subtype.
Researchers found no clear association between these chemicals and breast cancer overall.
The analysis included 1,609 breast cancer cases and 2,269 comparison participants.
The study used blood samples collected years before cancer diagnoses.
According to the research, women with the highest blood levels of PFOA had a 67% higher rate of estrogen receptor-negative (ER-negative) breast cancer than women in the lowest exposure group. For PFOS, the rate was 93% higher.
ER-negative breast cancer refers to tumours that lack receptors through which estrogen can promote cancer-cell growth. These cancers do not respond to hormone-based treatments such as anti-estrogen therapies in the same way as estrogen receptor-positive cancers. They also tend to be more aggressive and have worse outcomes.
The researchers measured 17 types of PFAS in blood samples collected years before the participants were diagnosed with cancer. The analysis included 1,609 women who developed breast cancer and a comparison group of 2,269 women.
Editorial Analysis
Why This Matters
The findings add to research examining how environmental exposures may be associated with specific types of cancer. ER-negative breast cancer has fewer established risk factors than some other breast cancer subtypes. Identifying possible environmental associations could help researchers better understand the factors involved in its development. The study also draws attention to the long-term presence of certain PFAS chemicals in the environment and the human body. Further research may help clarify whether exposure to these substances contributes to particular cancer outcomes.
The research drew on the Sister Study, a long-running investigation led by the NIH's National Institute of Environmental Health Sciences. The larger study enrolled women who did not have breast cancer at the time of enrolment but had a full or half-sister previously diagnosed with the disease.
Importantly, the researchers found no clear association between PFOA or PFOS levels and breast cancer overall. The reported percentages represent relative differences in the rates of ER-negative breast cancer between the highest and lowest exposure groups. They do not indicate an individual's absolute likelihood of developing the disease.
The researchers also compared their findings with previous research through a meta-analysis. The results supported an association between certain older PFAS chemicals and ER-negative breast cancer.
The study does not establish that PFOA or PFOS directly causes breast cancer. Researchers said further investigation is needed, particularly into newer PFAS chemicals that have replaced some older compounds.
