One in four cases of lung cancer affects people who have never smoked, it is not known why. Now, a study based on the genetic mutations of non -smoking tumors around the world reveals that the contaminated air we breathe can be the cause.
Although previous studies had demonstrated an epidemiological relationship between air pollution and lung cancer in non -smoking people, new research demonstrates for the first time that pollution damages DNA and that there is a genomic link in the air we breathe and lung cancer.
The study, published in Nature, was directed by Ludmil Alexandrov, from the University of California in San Diego (United States), and by Maria Teresa Landi, of the National Institute of American Cancer (NCI), and has the participation of scientists from the Spanish National Center for Spanish Oncological Research (CNIO) Pilar Gallego and Marcos Díaz-Gay.
A worrying trend
In recent years, lung cancer cases in people who have never smoked are increasing. This type of cancer especially affects Asian women and tends to be more regular in East Asia than in Western countries.
“We observe this worrying tendency that those who have never smoked develop more and more lung cancer, and we do not understand why,” says Ludmil Alexandrov.
“It is an urgent and growing world problem,” adds Landi, epidemiologist of the NCI cancer epidemiology and genetic division.
Until now, most previous studies on lung cancer do not differentiate between smokers and non -smoking data, and “has limited the identification of risk factors in these patients. Our study collects non -smokers data from around the world, and uses the genomics to trace which exhibitions could be causing these cancers,” he says.
To do the study, the team analyzed the lung tumors of 871 people who had never smoked and lived in 28 regions of Africa, Asia, Europe and North America with different levels of air pollution.
By sequencing the full genome they identified different DNA mutations patterns -known as mutational firms -, which become molecular traces of past environmental exhibitions.
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Combining the genomic data with estimates of air pollution, they discovered that those who lived in more polluted environments accumulated a significantly higher number of mutations in their lung tumors: they had 3.9 times more mutations related to smoking and 76% more mutations related to aging.
In fact, the study found that the more exposed a person was to pollution, he not only had more mutations in his cancer, but also had shorter telomers -the caps that protect the ends of the chromosomes -that it is a sign of cellular aging.
“In this study we have seen that the greater pollution, the greater the number of mutations, which does not mean that all the mutations will cause cancer, but some may be related to the carcinogenic process. And how many more mutations, the more possibilities there is that a bad is and the cancer develops,” explains Marcos Díaz Gay, head of the new Group of Digital Genomics of the CNI and first signature of the work.
In any case, “cancer is not just mutations, there are other immune processes that also influence but our study supports the hypothesis that the mutations associated with pollution could be an important risk factor,” he emphasizes.
The study identified another environmental risk: aristolochic acid, a carcinogen present in certain traditional medicinal herbs, which is responsible for a mutational firm that was found mainly in Taiwan patients who had never smoked.
Although this acid was previously related to bladder, gastrointestinal, renal and liver cancers due to ingestion, it is the first time it is related to lung cancer.
In addition, the group identified a new mutational firm of unknown origin and in greater proportion in lung cancers of non -smoking people with respect to smokers. The firm does not correlate with air pollution, or with any other known environmental exposure.
“We observe it in most cases of this study, but we still do not know why it is due. This is something totally different, and opens a completely new research area,” says Alexandrov.
“This mutational firm is very prevalent: in non -smokers it is present in 75% of cases, while in smokers it is only in 27% but, although today we cannot determine where it comes from, it is the one that generates the most mutations in non -smokers,” says Marcos Díaz.
In upcoming studies, researchers will include cases of lung cancer in non -smokers in Latin America, the Middle East and more regions of Africa.
In addition, “we want to continue this investigation by opening new ways to analyze other potential risks such as marijuana consumption or vapers and environmental risks such as radon gas, which we know is a risk factor for lung cancer that is not so well known today,” concludes Díaz-Gay.
With EFE information
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