LONDON, England, Tuesday November 8, 2016 – If you’re still smoking, quit now before it’s too late.
A new study of the devastating genetic damage, or mutations, caused by smoking shows a direct link between the number of cigarettes smoked in a lifetime and the number of mutations in the DNA of cancerous tumours.
The changes are permanent and persist even if a person gives up smoking, underscoring the importance of kicking the habit as early as possible.
In the study, which was published in the journal Science on Thursday, the highest mutation rates were seen in lung cancers, but tumours in other parts of the body – including the throat, bladder and liver – also had smoking-associated mutations, the scientists said.
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The research was carried out by an international group, including the Wellcome Trust Sanger Institute in Cambridge, England, and the Los Alamos National Laboratory in New Mexico, USA.
Joint lead author Professor Sir Mike Stratton, from the Wellcome Trust Sanger Institute, said: “The more mutations there are, the higher the chance that these will occur in the key genes that we call cancer genes, which convert a normal cell into a cancer cell.”
Smoking has been linked with at least 17 types of cancer, but until now scientists were not clear on the mechanisms behind many of them.
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Ludmil Alexandrov of Los Alamos National Laboratory explained that it had been difficult to explain how smoking increases the risk of cancer in parts of the body that don’t come into direct contact with smoke.
“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,” he said.
This study analysed over 5,000 tumours, comparing cancers from smokers with those from people who had never smoked.
It found certain molecular fingerprints of DNA damage – called mutational signatures – in the smokers’ DNA, and the scientists counted how many of these were in different tumours.
In lung cells, they found that on average, smoking a pack of cigarettes a day led to 150 mutations in each cell every year. Each mutation is a potential start point for a “cascade of genetic damage” that can eventually lead to cancer, they said.
Smoking a pack a day also led to an average 97 mutations in each cell in the larynx, 39 mutations for the pharynx, 23 for the mouth, 18 for the bladder, and six mutations in every cell of the liver each year.
Smoking kills six million people a year worldwide and, if current trends continue, the World Health Organization (WHO) predicts more than 1 billion tobacco-related deaths this century.