Alejandro Pérez Fidalgo
Medical doctor in the Oncology and Haematology Department at the Valencia Clinical Health Research Institute (INCLIVA), Valencia Clinical Hospital and member of the Long-Term Survivors and Adolescents and Young Adults working groups of the Spanish Society of Medical Oncology
It is a fact that the incidence of breast cancer is rising, and at an alarming rate amongst young people.
We do not actually know the direct cause, although the most plausible hypothesis is changes in lifestyle or exposure to carcinogenic agents such as chemicals.
The link between certain chemicals and breast cancer has been studied for decades, but it is very difficult to establish a direct causal link and determine whether these people have developed the disease as a result of exposure to such agents.
For this reason, I believe this is a highly relevant and interesting article. The article has cross-referenced and linked data from various US databases and agencies with chemical compounds that could trigger the onset of breast cancer or cause it to become more aggressive.
The fundamental limitation of the study is that it does not allow a clear causal link to be established directly, but it does generate a very strong hypothesis. For example, to identify the chemical compounds linked to breast cancer, they compiled a list based on experiments in mice (in vivo) or laboratory studies (in vitro) that had demonstrated or established a strong link between a chemical compound and breast cancer. From this list, based on data from various US agencies, they identified 921 chemical compounds that are potential causes of breast cancer.
With this list, the next step was to access another database in which they searched for those same compounds and determined where they had been identified – whether in food, drink, the air, pesticides, pharmaceutical products or even in building materials used in the US.
Finally, they accessed a third database from the NHANES agency (the US Centre for Disease Control’s National Health and Nutrition Examination Survey). This agency had carried out a study of chemical compounds in the blood and urine of numerous healthy individuals in the US.
Thus, whilst unable to establish a clear direct causal link, the authors have been able to formulate a strong hypothesis regarding which agents might cause breast cancer and where they originate from.
To arrive at this hypothesis, they adopted the following strategy: given a list of 921 chemicals identified in various experiments as potentially causing or inducing breast cancer, they set out to investigate the sources of exposure to these chemicals. In other words, they investigated where these chemicals have been found in the environment and checked whether they are present in food, water, soil, medicines, pesticides, etc., to which the population is exposed in their daily lives. Furthermore, mathematical modelling has been used to predict average exposure to these chemicals. This has been achieved by analysing databases that study the presence of these chemicals in the environment. And, finally, if these chemicals are found in the environment, they use the NHANES chemical biomonitoring database to check whether they have been detected in people’s blood and urine.
In this way, without directly establishing in a controlled experiment that a particular agent has caused the disease in specific individuals, the cross-referenced information from these three databases provides a strong hypothesis as to which chemicals and which sources of exposure we are subjected to could be responsible for breast cancer.
This is of great importance for making public health recommendations and reducing the levels of those chemicals that are most common or occur in higher concentrations, thereby preventing exposure amongst the general population.
Indeed, the study identifies chemicals that may be linked to breast cancer, either through their endocrine-disrupting effects (hormonal stimulation that increases cancer risk) or through genotoxicity (damage to cellular DNA that could also lead to cancer).
In particular, of the 921 substances studied, the most common sources of exposure were found to be everyday consumer products (500 chemicals), but 485 of these chemicals were also found in pesticides and 462 in food and drink (dietary products). Indeed, as many as 162 chemicals were even found in water.
In their mathematical prediction of which agents the population is most likely to be exposed to, they drew up a list of 50 chemicals, with ethanol—that is, the ethyl alcohol found in alcoholic drinks—standing out as the most common. The list includes compounds from the plastics industry, pesticides, cleaning products and pharmaceuticals, amongst others. Among these is a substance already known for having been studied for its potential impact on health: bisphenol A.
Strikingly, the authors have also identified which 19 substances on the list were present to some extent in the 200 most commonly prescribed medicines in the US in 2023.
Finally, when blood and urine samples from the NHANES dataset were analysed, six of the carcinogenic chemicals were found in more than 90 per cent of the blood samples, and several others in more than 95 per cent of the urine samples from the patients analysed.
Among the most notable chemicals were organophosphate pesticides such as malathion and DDT, a substance banned in the United States.
However, the main limitation is that the presence of these chemicals in the environment and in the blood does not necessarily mean they will cause breast cancer.
The levels of such exposure and individual susceptibility play a key role. We should therefore not be alarmed. It is true that we are surrounded by hundreds of compounds that could affect our health, but that does not necessarily mean they will cause us to develop cancer.
The study does not directly prove that these substances have caused cancer. However, it does suggest that it might be better to reduce exposure to these substances. In fact, the authors recommend taking various public health measures to reduce this exposure.
Attempting to minimise the presence of, and exposure to, these substances should be a public health priority for governments and health agencies. That is why this article is so relevant. It identifies sources of chemical compounds and demonstrates exposure to these agents that could cause cancer; therefore, advising the public to reduce or control this exposure should be the responsibility of the health authorities.
This study shows that establishing policies to control and reduce exposure to so many chemical agents should perhaps be given much higher priority than it currently is. We need to raise our own awareness and that of our governments and health authorities regarding the importance of trying to reduce exposure to the vast cloud of chemicals in which we live. Indeed, if exposure to these chemical agents continues to rise, it could pose a serious public health problem.
In a way, this study cannot provide an answer, but it does raise the question of whether exposure to so many chemicals could be behind the rise in cancer diagnoses identified over the last decade.