How fine particles trigger lung cancer in non-smokers

Air pollution linked to fine particles causes more than 250,000 deaths from lung cancer every year worldwide. And this, even in people who have never smoked. The observation was made, but the causal explanation was missing.

By what mechanisms do these fine particles act? The answer was unveiled on Saturday September 10, during the annual congress of the European Society for Medical Oncology, ESMO, which was held in Paris. “This study highlights an original model of cancer development”, comments Suzette Delaloge, medical oncologist, director of the personalized cancer prevention program at the Gustave-Roussy Institute, in Villejuif, who did not participate in this work. In the classic model, a toxin (like tobacco smoke) triggers mutations which, when accumulated, are enough to trigger cancer. But this is not the case for the subjects observed in this study: “It takes an extra step, which is inflammation. » Fine particles create this inflammatory process, which triggers the tumor transformation of only certain cells in the airways, those carrying risky mutations.

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Present in the exhaust gases of motor vehicles and in the fumes from the combustion of fossil fuels, fine particles are invisible to the naked eye. Their diameter is less than or equal to 2.5 micrometers – hence their name “PM2.5” – ie twenty to thirty times less than the diameter of a hair. “Because of this small size, they penetrate very far into the airways, in particular into the lungs”, explains Suzette Delaloge. These PM2.5 are responsible for approximately 14% of all lung cancer deaths. Tobacco, for its part, alone causes approximately 63% of these deaths.

Increasing proportion

In 2009, an American study estimated that 10% to 15% of lung cancers occur in non-smokers, but “this proportion is increasing”said Professor Charles Swanton, of the Francis Crick Institute and University College London (United Kingdom), during a press conference at ESMO.

The study that this renowned researcher conducted draws its strength from a combination of approaches and techniques, which range from epidemiology to cellular and molecular biology, including animal and human models.

First, epidemiology confirms the association between increased PM2.5 concentrations and the risk of developing various cancers. The authors analyzed data from 463,679 people residing in England, South Korea and Taiwan. By crossing individual PM2.5 exposure data – depending on where you live – and individual health data, they find that the risk of lung cancer increases by 16% for each increase of 1 microgram per cubic meter of PM2.5 rate. In addition, all the aerodigestive tracts are concerned. The risk increases by 15% for cancers of the lips, oral cavity and pharynx, by 26% for cancer of the larynx, by 30% for cancer of the small intestine and by 23% for cancer of the the anus. More surprising, because unrelated to the aerodigestive tract, it is increased by 19% for glioblastoma multiforme, a cancer of the central nervous system.

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