The researchers found that a biological switch is triggered after 25 years of consistent smoking that stimulates the growth of lung cells. Once activated, it is permanently on - and quitting tobacco will not turn it off. The result is that long-term smokers who give up the habit may be destined to develop lung cancer many years later. Now the discovery has been made scientists hope to find a way of de-activating the switch to halt the process, a little like defusing a ticking bomb.
Dr Jill Siegfried, who led the research at the University of Pittsburgh Cancer Institute, Pennsylvania, said: "Once this switch is turned on, it appears to be permanent, which may explain in part why long-term ex- smokers who have not had a cigarette in over 25 years are still at high risk for getting lung cancer."