In the 18th century, London surgeon Percival Pott noticedthat boys who cleaned chimneys were more likely to develop scrotal cancer later on. The doctor linked the development of the disease to the fact that chimney sweeps were exposed to soot. Now it’s soot located on the list of carcinogens.
Together with the EUSP Institute of Interdisciplinary Medical Research, we are looking into what this means and how such lists are compiled.
What are carcinogens
Oncological diseases arise due to errors in the process of cell division. This often happens randomly. Sometimes changes in cells are the result of exposure that damages DNA. This effect is caused, for example, by chemicals contained in tobacco smoke or ultraviolet radiation.
Carcinogens can include anything that, according to research, can increase the risk of cancer: products, physical and chemical substances, working conditions and other factors that a person encounters.
Researchers allocate Several possible mechanisms of carcinogenesis:
- Genotoxicity – ability to damage DNA. It is not necessary that a change in DNA become a mutation, that is, this factor may not be the main mechanism of carcinogenesis.
- DNA repair disorder — carcinogens affect DNA repair processes after damage.
- Chronic inflammation, which is caused, in particular, by the bacterium Helicobacter pylori. The process is believed to contribute to the initiation, development and progression of cancer.
- Immune system suppression allows tumor cells that arise under the influence of other mechanisms to escape immune surveillance.
- Immortalization cellsdue to which they acquire the ability to divide endlessly.
Determination of carcinogenic substances helps to develop measures for the prevention of cancer.
How do substances end up on the cancer-causing list?
The organization that compiles the list of carcinogens is the International Agency for Research on Cancer (IARC). This is a division of WHO works since the middle of the last century. Since 1971 IARC appreciated more than a thousand potential carcinogens, half of which were included in the list.
The list is compiled by independent experts. They collect and analyze the latest scientific data to evaluate its quality and decide whether there is enough information to add a new item to the list.
Expert group studies the following information:
- Evidence of whether a substance exhibits any of the recognized key characteristics of a human carcinogen.
- Experimental studies of cancer in laboratory animals exposed to a substance to evaluate mechanisms of carcinogenesis.
- Epidemiological studies of cancer in people exposed to a substance—quantifying the increase in risk in people exposed to a risk factor compared to a control group.
Experts are assessing whether there is a cause-and-effect relationship between exposure and the development of cancer. They are based on certain criteria. One of the first criteria lists offered Bradford Hill in 1965. Now they are still used, but taking into account new data and methods. Here some of them:
- The power of association. The stronger the association between exposure and disease, the more likely it is to be causal. Hill leads as an example of Percival Pott’s study on the incidence of scrotal cancer in chimney sweeps. The enormous strength of the association between this occupation and the disease—nearly 200 times stronger than in other occupations—led to the conclusion that chimney soot was likely a causative factor.
- Subsequence. The results are replicable across different groups of people, under different circumstances, and using different measurement instruments.
- Temporary relationships. Exposure always precedes disease.
- Dose-dependent effect. Increased exposure increases your risk of getting sick.
The criteria alone cannot answer the question of whether there is a causal relationship between exposure and disease development. But the totality of all the signs, as a rule, helps to make a judgment with one degree or another of convincingness.
After discussion, experts classify the substance under study into one of four categories.
1. Carcinogen
- Convincing evidence that the factor causes cancer in humans. That is, epidemiological studies have shown a cause-and-effect relationship between exposure to a substance and the development of cancer.
- Convincing evidence in animals.
- The substance has characteristics of carcinogens.
2A. Probable carcinogen
- Limited evidence of carcinogenicity to humans. This means that there is an association between exposure and cancer, but other causes cannot be ruled out.
- Sufficient evidence of carcinogenicity in experimental animals.
- Convincing evidence that the substance has key characteristics of a carcinogen.
2B. Possible carcinogen
One of the following results:
- Limited evidence of carcinogenicity in humans.
- Sufficient evidence of carcinogenicity in experimental animals.
- Convincing evidence that the substance has key characteristics of a carcinogen.
3. The substance cannot be classified as a carcinogen
The category is used when evidence of carcinogenicity to humans is insufficient and the rest is limited.
What is included in the list of carcinogens
You can view the full interactive list on the IARC website. Here are a few carcinogens from the first group:
- human papillomavirus,
- Helicobacter pylori,
- hepatitis B and C viruses,
- drinking alcoholic beverages,
- smoking tobacco,
- asbestos,
- radon,
- arsenic,
- formaldehyde.
Concerning non-ionizing radiation from mobile phones and sweeteners such as aspartame, are in this list in group 2B. This means that evidence of carcinogenicity in humans is limited. WHO didn’t change The conventional daily intake of aspartame per day is about 40 mg per kilogram of body weight. An adult weighing 70 kg will exceed this dose if he drinks 9-14 cans of soda per day.
Should you be afraid of cancer after exposure to a carcinogen?
Whether a person exposed to a carcinogen will develop cancer influences many factors including, for example, the amount and duration of exposure. IARC experts also clarifythat their classification does not indicate the level of risk. The likelihood of developing cancer associated with substances from the same group can be very different. Moreover, even a high risk does not mean that the event will definitely occur.
To increase the risk of cancer influence and other factors besides those we listed above:
- age;
- family history of cancer;
- overweight;
- ultraviolet radiation.
The first two factors are non-modifiable, that is, they cannot be influenced. The rest can be addressed by being physically active and using sunscreen.
There are many potential risk factors for cancer, but until we have evidence indicating a cause-and-effect relationship, their effect should not be overestimated. The best strategy is to focus on known factors and methods of prevention, and to be critical of the information about new carcinogens that often appears in the news.