Ex-smokers 'still more susceptible to lung cancer'
New research suggests that some of the genetic damage caused by smoking may never be reversed, despite the long-term health benefits of giving up.
A Canadian study published in the journal BMC Genomics analysed samples from the lungs of 24 current, former and non-smokers to identify patterns of gene activity.
The team, led by Wan L Lam and Stephen Lam from the BC Cancer Agency, found that some of the changes in gene activity caused by smoking were reversed by giving up the habit, including genes involved in mucus secretion.
However, other genes, including three required for DNA repair, were irreversibly damaged by smoking, and smoking was also found to switch off genes that help to prevent lung cancer.
Around nine in ten cases of lung cancer are caused by smoking, and half of newly-diagnosed cases occur in people who had previously given up smoking.
The researchers said that the findings help to explain why former smokers, although significantly healthier than current smokers, are still more susceptible to lung cancer than people who have never smoked.
First author Raj Chari commented: "Those genes and functions which do not revert to normal levels upon smoking cessation may provide insight into why former smokers still maintain a risk of developing lung cancer."
However, experts maintain that the health benefits associated with giving up smoking are significant and that the risk of developing lung cancer decreases cumulatively depending on the age at which a person gave up.
For example, a life-long male smoker has an estimated 16 per cent risk of developing lung cancer by the age of 75.
This risk falls to about 10 per cent for men who give up smoking at the age of 60, dropping to below 2 per cent for men who give up at 30.