CT lung cancer screening offers moderate benefit in smokers

June 16, 2008
Shalmali Pal

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

A new study finds that CT screening can reduce lung cancer mortality among smokers but won't 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 was published online by the RSNA June 11 and will appear 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 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 model of lung cancer development."The Lung Cancer Policy Model is a comprehensive microsimulation model of lung cancer development, disease progression, lung cancer detection, treatment results, and survival," McMahon's group said. "The model predicted diagnosed cases of lung cancer and deaths per simulated study arm (five annual screening examinations versus no screening)" McMahon is a senior scientist at the Institute for Technology Assessment at Massachusetts General Hospital. Her coauthors are from the departments of radiology and medicine at Harvard Medical School and Dana Farber Cancer Institute, both in Boston, University of Minnesota in Minneapolis, and Mayo Clinic in Rochester, MN.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%.

The simulation produced other results:

  • Non-small cell lung cancer detection was higher in the simulated screening arm.
  • NSCLC in the screening group was 3.6 times more likely to be stage I and 6.5 times less likely to be stage IV than cancers detected among subjects who were not screened.
  • Death caused by invasive staging or therapy for benign disease was 37% more likely in the screening population.

With regard to the last result, McMahon explained that the benefits of screening may still outweigh the risk of iatrogenic death.

"The risk of death due to invasive staging examinations strongly influences our predictions," she said. "Our modeling predicted that the number of lung cancer deaths avoided would exceed the number of iatrogenic deaths, but it's important to note that those benefits and risks were in different (hypothetical) people."In their

Radiology

paper, McMahon's group discussed why this study led to a middle-of-the road conclusion on the benefits of CT screening. 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 Dr. Peter Bach and colleagues from various institutions including Memorial Sloan-Kettering Cancer Center in New York City, however, noted that CT lung screening increased the rate of diagnosis and treatment but did not meaningfully reduce 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 endpoints. The I-ELCAP trial reported survival (the time between diagnosis and death, often expressed as the proportion of patients alive at a particular time point after diagnosis)," McMahon said. "Screening by its nature diagnoses cancers earlier so will yield a higher survival rate. Without a control arm, it is not possible to calculate changes in mortality due to screening."In comparison, McMahon explained that the current study and the Bach analysis reported the change in mortality rates (deaths in a fixed length of time from the beginning of the study) between the screening and (simulated) control arms. "The Bach study and ours differed in treatment of lung cancer deaths in the control arm during the first year of the study, leading to different conclusions," she said.For more information from the Diagnostic Imaging archives:

Tobacco money financed CT lung cancer screening trial

New CT lung screening study continues to skirt mortality issues

New data inflame debate over lung cancer screening

'Conflicting' CT lung trial data can be explained