The lung cells of people who smoke a pack of cigarettes a day are likely to develop 150 new genetic mutations every year, massively increasing their risk of lung cancer, according to a study published today in the journal Science. The researchers also found that cells in the larynx pick up 97 mutations, while those of the pharynx develop 39 mutations for every year of smoking that quantity of tobacco daily.
It’s no secret that smoking raises a person’s chances of developing cancer, with lung cancer being the most common due to the fact that inhaled smoke comes into direct contact with the pulmonary apparatus. In total, 17 different types of cancer are promoted by smoking, although until now scientists had not been able to observe the molecular causes of this link.
It is well established that cancer often results from genetic mutations, as damage to DNA causes abnormalities in the way that cells are able to replicate, sometimes causing them to start dividing in an out-of-control manner and develop into a tumor. Previous studies have shown that inhaling tobacco smoke promotes certain mutations in lung cells by causing damage to DNA, although the full extent of this effect had not been
An international team of researchers therefore decided to study cells from 5,243 tumors, some of which were from smokers while others were from non-smokers. By analyzing the genetic mutations in these tumorous cells, the study authors were able to figure out how much DNA damage can be attributed to smoking.
Their results showed a direct correlation between the number of years of smoking a pack a day and the number of genetic mutations in all tumor types. This effect was greatest in the lung cells, but was also noticeable in the mouth, where every cell had an average of 23 mutations per “pack year”, as well as the bladder and the liver, where cells picked up 18 and six mutations respectively for each year of such excessive smoking.
Study author Ludmil Alexandrov said in a statement that “before now, we had a large body of epidemiological evidence linking smoking with cancer, but now we can actually observe and quantify the molecular changes in the DNA due to cigarette smoking.”
Co-author Sir Mike Stratton added that “looking in the DNA of cancers can provide provocative new clues to how cancers develop and thus, potentially, how they can be prevented.”