Lung Cancer Risk Drops Within 5 Years of Quitting Smoking

Pam Harrison

June 01, 2018

Smokers who quit have a substantially lower risk for lung cancer than current smokers even within 5 years of stopping smoking, new research shows.

"If you smoke, now is a great time to quit," says lead author Hilary Tindle, MD, MPH, the William Anderson Spickard Jr professor of medicine, Vanderbilt University School of Medicine in Nashville, Tennessee.

"The fact that lung cancer risk drops relatively quickly after quitting smoking, compared to continuing smoking, gives new motivation," she said in a statement.

On the other hand, former heavy smokers still have over a threefold greater risk for lung cancer than those who never smoked for several decades after giving up the habit, the same research shows.

"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, MD, professor of medicine, Vanderbilt Center for Clinical Cardiovascular Outcomes Research and Trials Evaluation, Nashville, Tennessee.

The study was published online May 16 in the Journal of the National Cancer Institute.

Data from the Framingham Heart Study (FHS) Original as well as the FHS Offspring cohort were analyzed for lifetime smoking and lung cancer incidence from 1954 to 1958 for the Original cohort and between 1971 and 1975 for the Offspring cohort. Lung cancer rates were tracked through 2013.

Information on smoking habits was collected and participants were categorized as current, former, or never smokers. Some 3905 participants from the FHS Original cohort and 5002 participants from the FHS Offspring cohort were included in the analysis.

"Most people (89.5%) who were smoking at baseline quit during follow-up and never relapsed," the authors point out.

However, during a median follow-up of 25.1 years for the FHS Original cohort and 33.6 years for the FHS Offspring cohort, investigators documented 284 diagnoses of lung cancer.

"Among ever smokers, the majority of lung cancers (92.7%) occurred among heavy smokers, with 21.3 or more cumulative pack-years of smoking," researchers note.

In this subgroup of participants with 21.3 or more cumulative pack-years of smoking, the unadjusted lung cancer risk was greater than 10-fold higher compared with those who had never smoked.

Table. Incidence Rates of Lung Cancer

Smoking Category Incidence of Lung Cancer per 1000 Person-Years
Never smokers 0.26
Former smokers 1.61
Current smokers 1.97

Persistently Elevated

Investigators also observed that the risk for lung cancer among long-term former smokers remained "persistently elevated" even 25 years after quitting.

For example, among those who had stopped smoking for less than 5 years, the risk for lung cancer was over 12 times higher than it was for never smokers.

For the same long-term former smokers who quit smoking 5 to 9 years ago, the risk for lung cancer was still almost 12 times as high as it was for never smokers, while for those who hadn't smoked for 10 to 14 years, the risk for lung cancer was still almost 8 times higher than for never smokers.

For former heavy smokers who had stopped smoking 15 to 24 years ago, lung cancer risk was approximately 6 times higher than it was for those who never smoked, while for those who quit 25 years ago or more, the risk was over threefold higher, at a hazard ratio (HR) of 3.85, the researchers point out.

Importantly, 4 of every 10 lung cancers diagnosed in former smokers in the current study occurred in individuals who had stopped smoking over 15 years ago.

As such, these individuals do not quality for lung cancer screening, the study authors emphasize.

Lung Cancer Screening

Commenting on the findings in a related editorial, Erin Hahn, MD, and Michael Gould, MD, both from Kaiser Permanente Southern California, Pasadena, discuss the implications of the study's findings as they relate to current lung cancer screening guidelines.

As they point out, multiple guidelines, including the US Preventive Services Task Force, recommend annual screening with low-dose CT for people age 55 to 80 years who have a smoking history of 30 pack-years or longer and who currently smoke or who have quit smoking within the past 15 years.

Given these criteria, "a considerable percentage of current and former smokers who will receive a diagnosis of lung cancer may not be eligible for lung cancer screening," Hahn and Gould argue.

They also agree with the study authors that the persistently elevated risk for lung cancer in former heavy smokers as far out as 25 years after quitting is important.

"As the authors note, there are valid concerns about expanding current lung cancer screening eligibility," they acknowledge.

"Moreover, there is ongoing disagreement about whether the goal of a high-quality screening program is to identify the greatest number of treatable cancers or to maximize efficiency by providing screening services to those with the highest individual lung cancer risk," Hahn and Gould add.

The editorialists suggest that an "individualized" approach to lung cancer screening that takes into account multiple risk factors for lung cancer and not just smoking history might be the better way for physicians to make sure patients are appropriately screened, even though such an approach may not be covered by insurance policies.

The study authors have disclosed no relevant financial relationships. Gould reports receiving research support from Medial EarlySign to develop computer models of lung cancer risk. Hahn has disclosed no relevant financial relationships.

J Natl Cancer Inst. Published online May 16, 2018. Abstract, Editorial

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