“By changing our lifestyle, we can reduce our risk of cancer,” writes the Léon Bérard center on its site, on the occasion of World Cancer Day, this Saturday, February 4. In fact, it is estimated that in France “around 40% of cancers could be avoided by changing our behaviour”.
We know that alcohol and tobacco use can cause cancer, as can excessive consumption of red meat, but exposure to other substances in our environment can also be dangerous. However, being able to avoid or limit our contact with these products, it is still necessary to identify them.
The IARC (International Agency for Research on Cancer), a body of the World Health Organization, thus lists in its latest report 122 agents that are proven carcinogens, including opium and tobacco. It lists another 93 “probable” carcinogens and 319 “possible” carcinogens.
The European Union also has a similar classification of substances considered carcinogenic. This allows you to regulate or even prohibit its use and circulation in Europe.
“Possible”, “probable” or “proven” carcinogen?
To carry out this classification, these organizations study the scientific “packages of evidence” around the suspected substances, explains to BFMTV.com Henri Bastos, scientific director of Health and Work at ANSES (national health security agency).
His method “will mobilize three types of studies,” explains Béatrice Fervers, associate professor of oncology, head of the department of cancer prevention and the environment at the Léon Bérard center. There are “epidemiological studies, therefore in humans, experimental studies in laboratory animals, particularly in rodents, and studies in vitro in cell culture, to understand the mechanisms of action”, or laboratory tests.
For a product to be classified as “possibly carcinogenic“, “we rely on studies in humans and/or animals, but they are not convincing enough to classify the substance as a proven or probable carcinogen”, explains Henri Bastos. “The available information suggests a carcinogenic effect but is not conclusive”, summarizes the IARC.
A substance can be classified at the highest level, “probably carcinogenic”with, for example, conclusive studies on two animal species and the first positive epidemiological studies, but they have limits, continues Henri Bastos.
HE glyphosate is, for example, considered by the IARC as “probably” carcinogenic, an opinion “based on ‘limited’ evidence of cancer in humans and ‘sufficient’ evidence of cancer in laboratory animals.”
Because even if certain substances have “shown carcinogenic effects in the animal model”, which remains “strong evidence”, it is not enough to definitively decide, notes Béatrice Fervers: the carcinogenic effects observed in animals will not necessarily be the same in humans.
The category of proven carcinogens, “is used when there is sufficient evidence of carcinogenicity in humans.” “In other words, there is convincing evidence that the agent causes cancer in humans,” says the IARC.
And this convincing evidence is generally due to the positive results of epidemiological studies that “allow us to observe an association between exposure to a carcinogen and cancer risk,” says Béatrice Fervers. But the road to get there can be long.
substance = tumor? “It is not obvious”
First problem, it can be difficult to pinpoint the effect of a particular product in a study, because “we are exposed throughout our lives to a lot of things” that are potentially carcinogenic, Marc Audebert, INRAE’s director of research, told BFMTV.com. . Indeed, there are multifactorial causes of cancer: genetic, environmental, dietary, lifestyle… Intrauterine exposure can even be the cause of cancer.
In this sense, “it is not necessarily obvious to have a certain direct causal link: substance = tumor”.
Tobacco use, for example, is associated with several types of cancer. If there are smokers in a cohort, how do you know if their cancer potential is due to the item being tested and not tobacco? Therefore, several epidemiological studies with different, numerous audiences are necessary, and they present conclusions that go in the same direction.
“When we find in different studies, carried out in different countries or contexts, a positive association with this same carcinogen, we have a solid argument”, summarizes Béatrice Fervers.
What exposure to the substance?
There is also the question of the toxicity of a product and the dose to which the population is exposed. Marc Audebert takes the example of benzo(a)pyrene, a compound present in coal and oil. This product was pointed out for its danger after it was noted in the United Kingdom that chimney sweeps developed, proportionally, more tumors than the rest of the population.
“Historically, it is through the observation of populations of workers that we have acquired the greatest knowledge” about carcinogenic products, explains Henri Bastos.
In fact, the higher doses “of hazardous substances or compounds and the high frequency with which they may be exposed to them in industry may contribute to the onset of disease” more easily.
If the carcinogenic molecules “are used little and, therefore, there is a low exposure”, it is much more difficult to identify them, emphasizes Marc Audebert. But if they don’t present an immediate public health problem, it’s still important to identify them because they could one day be used in high doses in certain chemical processes.
Sometimes decades before an effect
Another difficulty for scientists: Cancer can appear several years after exposure to the carcinogen, even decades. Therefore, an epidemiological study can “require years” before reaching conclusions, which can be negative, explains Béatrice Fervers.
For all these reasons, patient cohorts are especially useful for researchers: hundreds, even thousands of people regularly provide very diverse data (places of residence, habits, diet, diseases, etc.) over several years, which can identify potential carcinogens. .
Béatrice Fervers also highlights the need to establish the carcinogenicity of a substance to show how it can cause cancer in the long term. A carcinogen can act by causing a DNA mutation, or chronic inflammation, or even affect the affected person’s immune response. And “many, do not act by a single mechanism”, but by “2, 3, 4, 5, 6 or 7” different mechanisms.
“If we don’t find the biological mechanism, we can say that (cancer) may be related to something else that hasn’t been measured,” says Béatrice Fervers.
“That explains why sometimes, even though we have arguments that tell us ‘there is something there’, we are not necessarily able to decide”, he concludes.
New methods under study
Today, “the important thing is to have as much knowledge as possible about the substances on the market in order to be able to identify toxic substances”, emphasizes Henri Bastos. And “the more time passes, the more the level of scientific knowledge increases, which allows us to refine our assessments and adapt the decisions that concern them.”
As the specialist points out, it is not necessary for a product to be classified as “proven carcinogen” to be subject to strict regulation or a ban, “classification as presumed carcinogen generally produces the same regulatory effects.”
Formaldehyde, used in particular in the manufacture of resins, was classified as a category 1B carcinogen (that is, probable carcinogen) in 2014 by the EU, but “in France, employers have been obliged to seek alternatives since the decree of 13 July 2006”. , indicates ANSES.
Researchers are currently working on new methods to identify cancer-causing molecules in our environment. This is the case of Dr. Marc Audebert, who launches tests to more quickly and definitively detect the carcinogenic potential of substances and this “without resorting to animal experimentation.”
Source: BFM TV
