Consuming a pack of cigarettes every day for a year can cause multiple changes in cells within various parts of the body, according to the study, published in the journal Science on Thursday.
The cells in parts of the body that are directly exposed to smoke are particularly damaged, with 150 mutations found to occur in lung cells within one year, 97 in the larynx and 39 in the oral cavity.
"I think one of the interesting things in this paper is the lack of methylation changes in tumor DNA related to smoking, when we do see significant changes in normal DNA between smokers and nonsmokers," said Dr. James Flanagan, a cancer geneticist at Imperial College London who was not involved in the study.
Flanagan's recent research has found that tobacco leaves a legacy on a smoker's DNA through methylation to influence whether genes are active or silent. He believes it's presumptive to say there's no role for methylation in these changes.
"I would assume that means the methylation is just so much more variable in tumors that the smoking-associated markers get lost in the statistical analysis. You can't argue from this that methylation changes from smoking are not important for cancer development."
But these new findings still shed valuable light on the way tobacco smoke increases the risk of cancer, particularly in parts of the body that are not actually exposed to smoke.
"The genome of every cancer provides a kind of 'archaeological record,' written in the DNA code itself, of the exposures that caused the mutations that lead to the cancer," said Sir Mike Stratton, director of the Wellcome Trust Sanger Institute in the UK, who co-led the research, in a statement. "Our research indicates that the way tobacco smoking causes cancer is more complex than we thought."
Stratton added, "this study of smoking tells us that looking in the DNA of cancers can provide provocative new clues to how cancers develop and thus, potentially, how they can be prevented."