Scientists have linked two "eternal chemicals" to an aggressive type of breast cancer

Scientists have linked high concentrations of two "eternal chemicals" in the blood with an increased incidence of breast cancer without estrogen receptors (ER-negative). When comparing participants from the United States and Puerto Rico with the highest and lowest levels of PFOS, the estimated incidence rate was 93% higher in the first group. For breast cancer in general, there was no clear association with these substances. About what the 93% estimate means and why scientists study different types of tumors separately, see the Izvestia article.

Where do the "eternal chemicals" come from in the body

The sources of exposure depend on the place where a person lives and works. In areas with polluted reservoirs or groundwater, drinking water may become the main route of entry. In other places, food products, including fish from polluted reservoirs, and household dust play a role. PFOA and PFOS have been replaced in many areas by other compounds, but previously released substances are still found in the environment.

How scientists tested the link with breast cancer

American epidemiologists used data from the Sister Study. From 2003 to 2009, the project included 50,884 women aged 35 to 74 from the United States and Puerto Rico. At the time of inclusion, the participants themselves did not have breast cancer. Everyone had a sibling with the same diagnosis. Therefore, the estimates obtained primarily apply to women with a family history of the disease.

Initial blood samples from 1,609 women who were subsequently diagnosed with breast cancer and 2,269 participants from a randomly selected subgroup were taken for analysis. It included 114 women who later became ill and were counted in both groups. Concentrations of 17 substances of the PFAS family were measured in the blood. Since blood was taken before diagnosis, the test results reflected previous exposure. The calculations took into account, among other things, smoking, physical activity and menopause.

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What does the indicator 93 mean?%

The participants were divided into groups according to the concentration of each substance in the blood. According to the authors' calculations, new cases of ER-negative cancer were 93% more common in the upper quarter of PFOS levels than in the lower quarter. For PFOA, the difference was 67%. The ratio of indicators for PFOS was estimated at 1.93, and the 95% confidence interval ranged from 1.15 to 3.22. Such a wide range shows that the magnitude of the connection has so far been determined with limited accuracy. The pattern of growth of the indicator during the transition from low to high concentrations was more convincing for PFOS.

The percentages describe the relative difference between the groups during the observation period. To estimate the absolute probability of the disease, it would be necessary to know the initial frequency of this type of tumor in a comparable population. Based on observational data, it is possible to estimate the strength of the connection. To find out whether substances are involved in the development of tumors, other studies are needed. In addition, one measurement in the blood only partially reflects the effects over a lifetime.

The authors also combined the results of seven studies in which PFAS concentrations were measured before diagnosis. For PFOA, the combined assessment indicated a 30% increase in the relative risk of ER-negative cancer. For PFOS, the estimate was 20%, while the confidence interval included the possibility of a lack of communication. How stable the result is for PFOS beyond the initial sample remains to be seen.

Why are the properties of a tumor important?

If the tumor cells carry an estrogen receptor, estrogen can stimulate their growth. This property is taken into account when choosing a treatment. Triple negative cancer belongs to the group of tumors without estrogen receptors. To classify it, doctors additionally evaluate progesterone receptors and the HER2 protein.

On average, ER-negative tumors are more aggressive. Relatively little is known about the risk factors for this group, said Alexandra White, head of the study and an epidemiologist at the National Institute of Environmental Sciences in the United States. The authors suggest that changes in gene regulation or the functioning of the immune system may be involved in the discovered relationship. These mechanisms will have to be tested separately.

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What is known about prevention

According to the classification of the International Agency for Research on Cancer, PFOA is classified as carcinogenic to humans, PFOS is classified as possibly carcinogenic. This classification reflects the strength of the evidence for the ability of a substance to cause cancer in principle. The assessment of the association with a breast tumor of a certain subtype requires separate data.

The researchers also suggest testing the results in groups with higher levels of exposure and among women without a family history of the disease.

Reducing contact with PFAS begins with clarifying the source. For example, in areas where drinking water is polluted, water analysis helps to determine which compounds are present in it. A blood test allows you to measure the concentrations of individual PFAS in the body. Such a test is not used to predict individual cancer risk, according to the US Agency for Registration of Toxic Substances and Diseases. Whether limiting contact with PFOA and PFOS will reduce the likelihood of ER-negative cancer remains to be seen.