Older smokers not subject to routine low-dose computed tomography (CT) screening were found to have 10 times the risk of lung cancer compared to never smokers, a cohort study found.
The U.S. Preventive Services Task Force (USPSTF) does not recommend annual lung cancer screening for former smokers age 50-80 years with 20 or more pack-years of smoking who quit 15 or more years ago or current smokers with less than 20 pack-years of smoking.
In the Cardiovascular Health Study (CHS), however, current non-heavy smokers with less than 20 pack-years of smoking had a significantly higher incidence of lung cancer over a median 13.3 years of follow-up (5.0% vs 0.5% for never smokers, adjusted HR 10.06, 95% CI 3.41-29.70), reported Ali Ahmed, MD, from the VA Medical Center in Washington, D.C., and colleagues.
As did former smokers with less than 15 years of smoking cessation (5.0%, adjusted HR 10.22, 95% CI 4.86-21.50).
“This [study] suggests that the lung cancer risk among heavy smokers may never drop to the level of never smokers, even after decades of smoking cessation, and highlights the importance of abstinence, early cessation, and possible screening,” the authors wrote in JAMA Oncology.
“Taken together, these findings suggest that current heavy smokers receive immediate risk reduction from smoking cessation but high-level risk persists despite very prolonged cessation. Yet this latter group of smokers is not currently considered for lung cancer screening,” they noted.
The authors suggested further studies be conducted to determine if low-dose CT might reduce lung cancer mortality in these lower-risk groups of smokers.
“For current smokers it is simple: encourage to quit and quit now. It is a bit more complicated for former heavy smokers who have quit 15 or more years ago for whom screening is not currently recommended. Given their 1,000% higher risk, it is tempting to recommend screening, but it will expose the 95% who do not develop lung cancer to harm of [testing],” Ahmed told MedPage Today.
In 2013, the USPSTF began recommending low-dose CT every year for high-risk current and former smokers age 55 to 80 years, resulting in more non-small cell lung cancer cases being caught while still at stage I in subsequent years.
Unsurprisingly, Ahmed’s group observed the greatest risk of lung cancer in current heavy smokers with at least 20 pack-years of smoking history (HR 39.29, 95% CI 20.24-76.25).
The cohort study was conducted using CHS data sets from the National Heart, Lung, and Blood Institute.
There were 5,888 community-dwelling individuals, 65 years of age or older, enrolled from June 1989 to June 1993. Participants averaged 72.8 years of age, and 57.3% were women. About five in six were white.
Baseline data on pack-year smoking history and duration of smoking cessation were required for analysis. Pack-years were defined by multiplying the number of packs (20 cigarettes) smoked per day by the number of years smoked at that level, summed over all levels of smoking.
Study authors acknowledged the lack of data on smoking habits during the follow-up period. Residual and unmeasured bias may have confounded results as well. Furthermore, cigarette use and lung cancers may have been underreported.
Finally, data from older smokers may not be generalizable to younger smokers, Ahmed and colleagues warned.
Ahmed reported being primary investigator and a co-investigator in multiple NIH and Veterans Administration Office of Research and Development funded projects, having paid full-time employment at the Washington D.C. Veterans Affairs Medical Center, and unpaid faculty appointments at George Washington University and Georgetown University.
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