A new statistical analysis of results from the National Lung Screening Trial (NLST) concludes that performing low-dose computerized tomography (CT) screening can be cost-effective compared to doing no screening for lung cancer in aging smokers.

“This provides evidence, given the assumptions we used, that it is cost-effective,” said second author Ilana Gareen, PhD, assistant professor (research) of epidemiology in Brown University’s School of Public Health in Providence, Rhode Island. The study was published in the New England Journal of Medicine (2014; 371:1793-1802).

Four years ago, the vast NLST showed that low-dose helical CT scanning reduced mortality from lung cancer by 20% compared to chest radiography. The study involved more than 53,000 smokers age 55 to 74 years. Chest radiographs, meanwhile, have been shown to be no better than doing nothing to screen for the cancer.

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With the NLST’s trove of medical and cost data to work from, a research team set out to determine the financial implications of conducting CT screening compared to not screening. The standard for this is to calculate a ratio of the costs of CT screening per person, which includes the test, any follow-up testing and treatment, and indirect costs, and the number of quality-adjusted life-years added per person across the population. The quality adjustment distinguishes between living in good health and surviving but with major health problems.

The resulting ratio was $81,000 per quality year added. A standard accepted value is that any sum below $100,000 is cost-effective.

The researchers concluded that, “whether screening outside the trial will be cost-effective will depend on how screening is implemented.” This is because, like all cost-effectiveness analyses, the derivation of the $81,000 ratio involved many assumptions.

When the researchers varied their assumptions or conducted analyses of cost-effectiveness in some subgroups of patients, they found that the resulting ratios varied widely, sometimes improving but sometimes reducing the cost-effectiveness.

Here is one example: In the main analysis researchers assumed that there was no life-prolonging medical benefit to CT screening other than detecting lung cancer. But when they factored in a different assumption, which was that other serious conditions would be detected and treated (as happened during the NLST), then the ratio fell to $54,000 per quality-adjusted life-year added.

They also saw the ratio become more favorable when they assumed that some diagnoses of lung cancer assumed to be excess (diagnoses beyond the rate that is expected in the population) were cancers that would have impacted participant life expectancy, as opposed to being benign forms of lung cancer.

But other changes in assumptions brought the ratio above or near the $100,000 cutoff. Examples included adding in the future health costs for survivors, assuming higher costs than in the study for screening, follow-up, or treatment, or more pessimistic assumptions about survival or quality of life. When the cost for the test reached $500 (compared to the $285 it cost in the NLST), then cost-effectiveness eroded.

How the screening is implemented matters, Gareen said, because while CT scanning has a demonstrated medical benefit, paying for it means potentially not paying for something else.

“Cost is becoming more and more important, and if you fund one thing, there are other things you won’t be able to fund,” Gareen said.