Study Fuels Lung Cancer Screening Debate

Jumping into the ongoing controversy about widespread lung cancer screening, a new study concludes that if older heavy smokers or former smokers in the United States had low-dose computed tomography (LDCT) screening for lung cancer, about 12,000 lives could be saved each year. However, after factoring in the numerous false-positive results that lead to follow-up testing or unnecessary biopsies, the additional cost of screening for each life saved could be $240,000.

Investigators from the National Lung Screening Trial (NLST) reported in 2011 that LDCT screening reduced lung cancer deaths by 20% compared with standard X-ray screening over about 7 years among more than 53,000 people at high risk for lung cancer. However, the number of deaths that might be averted by implementing the trial's screening regimen nationwide wasn't examined.

For the current study, the results of which are published in Cancer, Jiemin Ma, PhD, and Ahmedin Jemal, PhD, of the American Cancer Society in Atlanta, GA, and their colleagues used the same eligibility standards for screening as did the NLST. They drew on U.S. Census data and other national reports about smoking prevalence and mortality to estimate that 8.6 million current and former smokers ages 55 to 74 would be eligible for screening with LDCT and that doing so would avert approximately 12,000 deaths a year in the United States.

In an accompanying editorial, Larry Kessler, ScD, of the University of Washington School of Public Health in Seattle, asks whether saving 12,000 lives a year from lung cancer is sufficient to justify widespread screening and whether health policy makers and clinicians would embrace such an effort.

Lung cancer kills about 158,000 people in the United States each year, and if the new study's estimates are correct, LDCT screening could prevent about 7.6% of those deaths.

However, LDCT screening would come at a cost. In the NLST trial, the rate of positive screening tests was 24.2% with LDCT; 96.4% of those results were false positives that detected perhaps a benign lesion, inflammation, or a radiographic shadow. (In comparison, the rate of positive screening tests was 6.9% with X-ray imaging, 94.5% of which were false positives.)

“CT scanning does pick up early lesions and can save lives through earlier diagnosis, albeit at an extraordinary cost given the number of false positives that need evaluation,” says Daniel Haber, MD, PhD, director of the Massachusetts General Hospital Cancer Center, who was not involved in the study.

Haber suggests that in the future, complementary imaging technology, such as functional approaches to detect tumor metabolism, could help refine the CT diagnosis. Molecular methods for detecting cancer, such as by capturing circulating tumor cells or traces of tumor DNA in the bloodstream, could enhance the predictive value of the CT test. Both approaches could reduce the number of false positives—and improve the cost/benefit equation—but neither is currently clinically available.

So for now, whether to begin routinely screening smokers for early lung lesions depends on the merits of LDCT alone. The limitations of screening, writes Kessler, highlight the ongoing need for smoking cessation and prevention programs, which have the potential to save many more lives than screening.