Tobacco: Smokers trigger cancer countdown

People who smoke for 25 years or more may start a countdown to lung cancer that cannot be stopped by giving up cigarettes, scientists said yesterday. But anti-smoking groups warned that the findings should not be seen as an excuse for not bothering to quit. They said that other studies had shown the benefits of stopping.

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."