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Scientists have long known that air pollution may be linked to an increased risk of lung cancer in people who have never smoked, but new research describes a mechanism that may help explain how.
The findings, presented at the European Society for Medical Oncology’s Presidential Symposium in Paris on Saturday, suggest air pollution can trigger lung cancer in people who haven’t smoked because some air pollutant particles can promote changes in cells in the airways.
In particular, greater exposure to fine dust, or particulate pollution in the air — 2.5 microns in diameter or smaller — can cause rapid changes in airway cells that have mutations in a gene called EGFR, which occurs in about half of people with lung cancer never smoked, and another gene linked to lung cancer called KRAS, according to research conducted by scientists at the Francis Crick Institute in London and other institutions around the world.
“We found that driver mutations in EGFR and KRAS genes, which are common in lung cancer, are actually present in normal lung tissue and are a likely consequence of aging,” Charles Swanton, scientist at the Francis Crick Institute and senior clinician at Cancer Research Britain, which presented the results, said in a press release on Saturday.
“In our research, these mutations alone have only weakly potentiated cancer in laboratory models. However, when lung cells with these mutations were exposed to air pollutants, we saw more cancers and they occurred faster than when lung cells with these mutations were not exposed to pollutants, suggesting that air pollution promotes the development of lung cancer in cells harboring gene mutations in drivers.” said Swanton. “The next step is to find out why some lung cells with mutations become cancerous when exposed to pollutants, while others do not.”
Particulate matter, or particle pollution, in the air is a mixture of solid particles and liquid droplets, according to the US Environmental Protection Agency. Some are emitted in the form of dirt, dust, soot or smoke and can come from coal and natural gas power plants, cars, agriculture, dirt roads and construction sites, among others.
Researchers analyzed data from 463,679 people to find associations between their exposure to air pollution and cancer risk.
At 2.5 microns (PM 2.5) in diameter or smaller, particulate matter is the smallest air pollutant, yet one of the most dangerous. When inhaled, these pollutants can penetrate deep into the lung tissue, where they enter the bloodstream and can contribute to asthma, cardiovascular disease, and other respiratory diseases.
As part of their analysis, the researchers found that rising air pollutant levels at PM 2.5 have been associated with an overall increase in the risk of EGFR-related non-small cell lung cancer in England, South Korea and Taiwan. Up to 33% of normal lung tissue samples in the study contained driver mutations in EGFR and KRAS, even in the absence of cancer.
“First, we look at the epidemiological data on air pollution and lung cancer risk among non-smokers and find a good correlation in England, South Korea and Taiwan,” Swanton said in a video released by the European Society for Medical Oncology on Saturday.
“Second, we use animal models to show that when we expose mice to environmental pollution — these mice are susceptible to mutations in either EGFR or KRAS — we see a dramatic increase in the number, size, and severity of cancers in these mice after they get the.” exposed to pollution,” he said.
The researchers examined 247 normal lung tissue samples, examined tissues from humans and mice after exposure to air pollutants, and then studied the consequences of that exposure in the mouse models.
“What we found is that exposure to air pollution leads to an inflammatory axis in both mice and humans,” which transforms cells, Swanton said in the video.
“And it’s only when that stem cell has an EGFR mutation that a tumor is initiated,” he said. “What we found when biopsying normal lung tissue is that EGFR and KRAS mutations in normal lung tissue occur in over 50% of normal lung biopsies, and these occur with age.”
These mutations in the EGFR and KRAS genes “may very well be why the non-smoking population eventually develops lung cancer. This question has occupied us for a number of years: Why do people who are otherwise healthy and have no connection to second-hand smoke or primary smoking still develop lung cancer? American Lung Association chief medical officer Albert Rizzo told CNN Monday.
“So we know that air pollution was listed as a carcinogen by the World Health Organization a few years ago, and I think this study just adds evidence that it’s a specific mechanism for these PM 2.5 particles to contribute Development of lung cancer leads this population,” said Rizzo, who was not involved with the research.
“We should really make sure that we limit PM exposure as much as possible,” he added. “We don’t have much control over our genetics right now, but we can control air pollution.”
Research has found this exposure to PM 2.5 air pollution can be linked to lower lung function and an increased risk of cardiac arrest, among other health problems. A study published in the Proceedings of the National Academy of Sciences in 2019 estimated that particulate matter in the air was responsible for 107,000 premature deaths in the United States in 2011 and cost society $886 billion.
“The same airborne particles that come from burning fossil fuels and exacerbate climate change directly impact human health through an important and previously overlooked carcinogenic mechanism in lung cells,” Swanton said in the press release.
“The risk of lung cancer from air pollution is lower than from smoking, but we don’t have control over what we all breathe,” he said. “Globally, more people are exposed to unsafe air pollution than toxic chemicals in cigarette smoke, and this new data links the importance of climate health to improving human health.”
The new research suggests that rather than causing mutations in cells that lead to cancer, airborne PM 2.5 pollutants may turn on existing mutations, Richard Smith, chair of the UK Health Alliance on Climate Change, wrote in an opinion article in of the medical journal BMJ on Monday.
“This mechanism may be important in other cancers with carcinogens other than air pollution,” Smith wrote.
“The usual invisibility of current air pollution must help prevent us from giving it the attention it deserves, but the roots of medicine’s neglect of air pollution must lie in the intertwined factors of the feeling that doctors are doing nothing about air pollution skills and failures in the training of physicians,” he wrote.
“There is advice doctors can give individuals – to recognize the importance of polluted air, reduce internal pollution in the home, access information about local air pollution, change travel itineraries, avoid particularly toxic days and maybe even reduce the problem.” to contribute by driving less or not at all – but the necessary response is policy action at the local, national and global levels.”
