Like “a hidden killer”, air pollutants can cause lung cancer in non-smokers via a mechanism revealed on Saturday in a study, which marks an “important step for science and society” according to experts.
Already involved in climate change, fine particles – less than 2.5 microns, about the diameter of a hair – are responsible for cancerous changes in cells of the respiratory tract, according to scientists from the Francis-Crick Institute and from University College London.
Present in exhaust fumes, dust from vehicle brakes or fumes from fossil fuels, fine particles are “a hidden killer”, Charles Swanton of the Francis-Crick Institute, in charge of research, told AFP. present this research, not yet peer-reviewed, at the annual congress of the European Society for Medical Oncology, which took place in Paris.
While air pollution has long been suspected, “we weren’t sure if this pollution directly caused lung cancer, or how,” said Professor Swanton.
The researchers first explored data from more than 460,000 residents of England, South Korea and Taiwan, and showed that exposure to increasing concentrations of fine particles was linked to an increased risk of lung cancer.
The major discovery is that of the mechanism by which these pollutants can trigger lung cancer in non-smokers.
Through laboratory studies on mice, the researchers showed that the particles caused changes in two genes (EGFR and KRAS), already linked to lung cancer.
They then analyzed nearly 250 samples of healthy human lung tissue, never exposed to carcinogens from tobacco or heavy pollution. Mutations in the EGFR gene appeared in 18% of the samples, alterations in KRAS in 33%.
“On their own, these mutations are probably not enough to lead to cancer. But when you expose a cell to pollution, it probably stimulates some kind of “inflammatory” reaction, and if “the cell harbors a mutation, it will form cancer”, summarizes Professor Swanton.
It is a “deciphering of the biological mechanism of what was an enigma” but “quite confusing”, recognizes this chief medical officer of Cancer Research UK, the main funder of the study.
Traditionally, it was thought that exposure to carcinogenic factors, such as those from cigarette smoke or pollution, caused genetic mutations in cells, making them tumorous and causing them to proliferate.
For Suzette Delaloge, director of the cancer prevention program at the Gustave-Roussy Institute, “it’s quite revolutionary because we had practically no demonstration before of this alternative carcinogenesis”.
“This study is a fairly important step for science – and for society too, I hope,” said the oncologist, responsible for discussing the study at the congress. “This opens a great door for knowledge but also for prevention”.
The next step will be to “understand why certain altered lung cells become cancerous after exposure to pollutants”, according to Professor Swanton.
This study confirms that reducing air pollution is also crucial for health, insist several researchers.
“We have a choice whether or not to smoke, but not the air we breathe. As probably five times more people are exposed to unhealthy levels of pollution than tobacco, this is a major global problem,” launched Professor Swanton.
More than 90% of the world’s population is exposed to what the WHO considers to be excessive levels of fine particulate pollutants.
This research also gives hope for new approaches to prevention and treatment.
To detect and prevent, Suzette Delaloge is considering several avenues but “not for tomorrow”: “personal assessment of our exposure to pollutants”, detection – not yet possible – of the EGFR genetic mutation, etc.
For Tony Mok, from the University of Hong Kong, quoted in an ESMO press release, this research, “as intriguing as it is promising”, “allows us to consider one day looking for precancerous lesions in the lungs using imaging and then trying to treat them with drugs like interleukin-1 inhibitors.”
Professor Swanton imagines “what molecular cancer prevention could look like in the future, with a pill, perhaps every day, to reduce the risk of cancer in high-risk areas”.