Lung cancer risk drops substantially within 5 years of quitting smoking: study

New research has found that quitting smoking can substantially reduce the risk of lung cancer within five years although also warns that ex-smokers still have a greater risk of the disease even years later.

Carried out by researchers at Vanderbilt University Medical Center in Nashville, Tennessee, the study used data taken from the landmark Framingham Heart Study, which records the health information of residents in Framingham, Massachusetts, to look at high blood pressure and high cholesterol as key risk factors for cardiovascular disease, as well as tracking cancer outcomes.

The Framingham study is also unique because it asked people about their smoking every two to four years, therefore looking at any increases or decreases in smoking over time.

For the new study, the researchers looked at data from 8,907 participants who had been followed for 25 to 34 years.

Of the 284 lung cancers which were diagnosed during this time, nearly 93 percent occurred among heavy smokers, defined as those who had smoked at least a pack of cigarettes a day for 21 years or more.

However, the team also found that former heavy smokers showed a 39 percent reduction in their risk of developing lung cancer just five years after quitting, when compared to current smokers.

This risk also continued to fall as the years passed.

"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," she said.

The researchers also cautioned however, that four of 10 cancers in heavy smokers occurred more than 15 years after they quit, and ex-smokers still had a threefold higher risk of lung cancer than those who had never smoked even 25 years after quitting.

"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 results can be found published online in the Journal of the National Cancer Institute.