Why don’t most smokers get lung cancer?

Tobacco is an important risk factor for lung cancer. The harmful substances contained in cigarettes promote the appearance of DNA mutations. However, heavy smokers do not necessarily carry more mutations than others according to a study published in Nature Genetics. How to explain this?

Although tobacco is responsible for the majority of lung cancers, only a minority of smokers develop the disease. There are approximately 13 million smokers in France, for 46,000 lung cancers (nearly 90% due to tobacco) diagnosed each year. Researchers from thealbert Einstein College of Medicine suggest, in a study published in Nature Geneticsthat some smokers have a system of prevention mutations more robust than the others. Explanations.

Tracking DNA mutations caused by tobacco

The specialists of cancer Lung scientists have long suspected that cigarette smoke promotes cancer by causing mutations in the DNA of lung cells — which, accumulating over time, turn them into malignant cells. This assertion remained difficult to prove because of technical limitations. ” But that could never be proven until this study, because there was no way to quantify mutations in normal cells. says Jan Vijg, Ph.D., co-lead author of the study.

What the researchers lacked was the ability to sequence the entire genome of an isolated cell without the sequencing itself does not induce mutations which are then difficult to distinguish from the real mutations caused by cigarette smoke. The technique that researchers of theAlbert Einstein College of Medicine have improved door the name of SCMDA. It was applied to the bronchial basal cells of 33 participants, aged 11 to 86, with more or less significant smoking history. ” These lung cells can survive for years, even decades, and therefore can accumulate mutations with age and smoking. »

The appearance and the accumulation of mutations in the DNA is a normal process, but exposure to cigarette smoke, and its approximately 4,000 harmful substances, significantly increases the frequency of these phenomena. It seems clear that long-time smokers accumulate more mutations, which increase the risk of cancer. However, this is not what the scientists observed. ” The heaviest smokers did not have the highest number of mutations. Our data suggest that these individuals may have survived so long, despite their heavy smoking, because they managed to prevent the accumulation of additional mutations.. »

Repair Mutations

This observation opens up new avenues of research on the effectiveness of DNA repair mechanisms. To date, it is difficult to estimate an individual’s DNA repair capacity, but scientists hope to develop a test that will make this possible. This could then become a means of evaluating each person’s risk of developing lung cancer in addition to parameters already known such as the duration of smoking, the age of the first cigarette or the number of packages dailies.