Lung Cancer Risk Drops Quickly After Quitting Smoking, But Persists.

A new study co-authored by a School of Public Health researcher has found that the risk of developing lung cancer drops substantially after someone quits smoking, but is still elevated many years later.

The study, published in the Journal of the National Cancer Institute, finds lung cancer risk decreases by 39 percent five years after quitting smoking, but after 25 years is still three times the risk of someone who never smoked.

“These data underscore a potential need for screening former heavy smokers for lung cancer risk beyond the currently recommended time period of 15 years,” says co-author Vasan Ramachandran, professor of medicine at the School of Medicine and of epidemiology at SPH.

The researchers conducted an analysis of the BU-based Framingham Heart Study, one of the world’s longest-running studies on cardiovascular disease. The study, which is supported by the National Heart, Lung, and Blood Institute, helped establish high blood pressure and high cholesterol as key risk factors for cardiovascular disease.

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.

The Framingham Heart 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.

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.

Current federal guidelines, which mandate insurance coverage of lung cancer screening for current and former smokers, exclude those who have not smoked for 15 years or more. Yet 4 of 10 cancers in heavy smokers in the current study occurred more than 15 years after they quit. 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.

The study was led by Matthew Freiberg and co-authored by Hilary A. Tindle, Pierre Massion, Robert Greevy, Meredith Stevenson Duncan, and Suman Kundu, all of Vanderbilt University Medical Center.