A team of scientists from a number of international institutions have found that smoking can cause over a hundred mutations in the cells of the body every year and that these changes are permanent. The study is available to read in the peer-reviewed journal, Science, on an open access basis.
The genetic study examined the DNA mutations found in the many different types of cancer cell that are caused by smoking. It compared DNA sequences in over 5,000 cell samples from lung, throat, mouth, kidney, liver, pancreatic, bladder and cervical cancers which have all been linked to smoking. Almost 2,500 samples had been provided by people who smoke and just over 1,000 of the samples were from people who had never smoked. This enabled the scientists to compare the number and types of mutations found in non-smokers and smokers.
The scientists found that the DNA cells from the patients who smoked had a greater number of mutations, particularly in throat, lung, liver and kidney cancer. Certain mutations appeared more often, particularly in throat and lung cancers. Some of the non-smokers also had these mutations, but the researchers guessed that these could have been caused by previous smoking habits that had not been reported or by passive smoking. The scientists used the information they found in the study to calculate an age-adjusted risk of someone developing a specific cancer, who smoked 30 plus cigarettes a day. They suggested that a male smoker was 13 times more likely to develop cancer of the larynx and 22 times more likely to develop adenocarcinoma, the most frequent type of lung cancer. They also used the data to calculate how many mutations would be developed by a person smoking one pack of cigarettes a day for a year. They suggested that this could cause 97 mutations in the larynx, 39 in the pharynx, 23 in the cells of the mouth, 150 mutations in the lung cells, 18 in the bladder and 6 in the cells of the liver.
The scientists concluded from their study that smoking causes cancer by increasing the number of mutations at DNA level, although this study was not able to show how this happens. The study highlights the dangers of cigarette smoking. Many cell samples were analysed during this study and the cell mutations were compared between non-smokers and smokers. Even in cancer of the same type, there were variations. Samples from smokers often had more mutations and abnormal substitutions when their DNA sequence was examined. This study cannot make predictions or prognosis based on these mutations alone because other factors such as alcohol consumption may also have an effect. The results produced by this study are very general estimates because of other factors such as environment, lifestyle and type of tobacco smoked, may all have a bearing on the number of mutations in a person’s DNA.
However the known harms of cigarette smoking are added to by this study. The habit is harmful, both to the smokers themselves and their loved ones who live with them. More research may be needed to understand the mechanisms by which these cell mutations cause the cancer, but the message remains the same: to reduce the risk, it would be best to give up smoking altogether.
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Alexandrov L.B., et al. Mutational signatures associated with tobacco smoking in human cancer, November 2016, Science, Vol.354, Issue 6312, pp.68-622