CT lung screening offers moderate benefit to smokers

A new study finds that CT screening can reduce lung cancer mortality among smokers but will not protect them from the other adverse effects of lighting up.

Results from an evaluation of the long-term efficacy of screening fell between more positive outcomes reported by the International Early Lung Cancer Action Program (I-ELCAP) and another investigation that declared CT screening was not entirely advantageous. The latest study appears in the July issue of Radiology (2008;248[1]:278-287).

"Smoking cessation should be the primary message to any continuing smokers," lead investigator Pamela McMahon, Ph.D., told Diagnostic Imaging. "Our analysis suggests that lung cancer screening may offer some additional benefit, but patients should be made aware that our study was a modeling study, not a randomized clinical trial."

McMahon, a senior scientist at the Institute for Technology Assessment at Massachusetts General Hospital, and colleagues took data concerning 1520 current and former smokers, screened as part of the Mayo Clinic helical CT trial, and used the information to populate a Lung Cancer Policy Model, a comprehensive microsimulation model of lung cancer.

The initial data were compiled from the Mayo Clinic's single-arm evaluation of helical CT in current and former smokers (61% of the total study population). All patients underwent baseline screening and four annual CT exams. Nodules found on a screening exam were followed up with thin-section CT imaging.

At six-year follow-up in the simulation, the screening arm had an estimated 37% relative increase in lung cancer detection compared with subjects who had not been screened. Lung cancer-specific mortality was 28% lower in subjects who received CT screening, while all-cause mortality was 4% lower, compared with subjects who were not screened. At 15 years, the relative reduction in lung cancer-specific mortality was 15%, and the reduction in all-cause mortality was only 2%.

McMahon's group discussed why this study led to a middle-of-the road conclusion. I-ELCAP results predicted that 80% of people whose lung cancer was caught early with CT screening could expect to live at least another decade (Radiology 2007; 243[1]:239-249; NEJM 2006;355[17]: 1763-1771). A longitudinal analysis by a multi-institution group led by Dr. Peter Bach of Memorial Sloan-Kettering Cancer Center in New York City, however, noted that CT lung screening showed no meaningful reduction in the risk of advanced lung cancer or death from lung cancer (JAMA 2007;297[9]: 953-961).

"These three studies did use entirely different methods, but I would argue that the differences in results are due more to differences in reporting of end points," McMahon said.

-By Shalmali Pal