National Lung Screening Trial

The National Lung Screening Trial (NLST) compared two ways of detecting lung cancer: low-dose helical computed tomography (CT)—often referred to as spiral CT—and standard chest X-ray. Helical CT uses X-rays to obtain a multiple-image scan of the entire chest, while a standard chest X-ray produces a single image of the whole chest in which anatomic structures overlie one another.

The study findings reveal that participants who received low-dose helical CT scans had a 15 to 20 percent lower risk of dying from lung cancer than participants who received standard chest X-rays. This is equivalent to approximately three fewer deaths per 1,000 people screened in the CT group compared to the chest X-ray group over a period of about 7 years of observation (17.6 per 1,000 versus 20.7 per 1,000, respectively).

On average over the three rounds of screening exams, 24.2 percent of the low-dose helical CT screens were positive and 6.9 percent of the chest X-rays were positive. In both arms of the trial, the majority of positive screens led to additional tests.

Adenocarcinomas and squamous cell carcinomas were detected more frequently at the earliest stage by low-dose helical CT compared to chest X-ray. Small-cell lung cancers, which are very aggressive, were infrequently detected at early stages by low-dose helical CT or chest X-ray.

NLST Study Facts

NLST enrolled 53,454 current or former heavy smokers ages 55 to 74. Participants were required to have a smoking history of at least 30 pack-years and were either current or former smokers without signs, symptoms, or history of lung cancer. Pack-years are calculated by multiplying the average number of packs of cigarettes smoked per day by the number of years a person has smoked. Participants were randomly assigned to receive three annual screens with either low-dose helical CT or standard chest X-ray.

Launched in 2002, the initial findings were released in November 2010. On June 29, 2011, the primary results were published online in the New England Journal of Medicine and appeared in the August 4, 2011, print issue.

NLST was conducted by the American College of Radiology Imaging Network, a medical imaging research network focused on the conduct of multicenter imaging clinical trials, and the Lung Screening Study group, which was initially established by NCI to examine the feasibility of NLST.