Washington, May 30: Just because you stopped smoking years ago doesn't mean you're out of the woods when it comes to developing lung cancer. However, there is still a ray of hope. According to a study conducted by the Vanderbilt University Medical Center, the risk of lung cancer drops substantially within five years of quitting.

"If you smoke, now is a great time to quit," said first author Hilary Tindle. "The fact that lung cancer risk drops relatively quickly after quitting smoking, compared to continuing smoking, gives new motivation". Tindle and her colleagues examined the health records of residents of Framingham, Massachusetts, who have been followed for decades by the Framingham Heart Study.

The study helped establish high blood pressure and high cholesterol as key risk factors for cardiovascular disease. But it also tracked cancer outcomes. The current study looked at 8,907 participants who had been followed for 25 to 34 years. During this period, 284 lung cancers were diagnosed, nearly 93 percent of which occurred among heavy smokers, those who had smoked at least a pack of cigarettes a day for 21 years or more.

Five years after quitting, the risk of developing lung cancer in former heavy smokers dropped by 39 percent compared to current smokers and continued to fall as time went on. Yet even 25 years after quitting, their lung-cancer risk remained over threefold higher compared to people who had never smoked.

The study is unique because it asked people about their smoking every two to four years, and could account for increases or decreases in smoking over time. Further study is warranted to determine whether extending the cut-off point for mandated screening would be cost-effective and save lives, the researchers concluded.

"While the importance of smoking cessation cannot be overstated, former heavy smokers need to realize that the risk of lung cancer remains elevated for decades after they smoke their last cigarette, underscoring the importance of lung cancer screening," said senior author Matthew Freiberg.

The findings from the study are published in the Journal of the National Cancer Institute.