On Sept. 18, 2002, the National Cancer Institute (NCI) launched the National Lung Screening Trial to compare two ways of testing for early lung cancer in current and former heavy smokers: spiral computed tomography and single-view chest x-ray. Both spiral CT scans and chest x-rays have been used in clinical practice to detect lung cancer in asymptomatic individuals, but scientific evidence is inconclusive as to whether screening for lung cancer with either method will reduce lung cancer mortality. The trial will examine the relative risks and benefits of both tests in 50,000 current and former smokers at 30 study sites throughout the U.S.

The NLST researchers found approximately 15 percent to 20 percent fewer lung cancer deaths among trial participants screened with low-dose helical CT relative to chest X-ray. This finding was highly significant from a statistical viewpoint, meaning it was due not to chance but rather to screening with helical CT. The 15 percent to 20 percent lower lung cancer death rate is equivalent to approximately three fewer deaths per 1,000 people screened in the CT group compared to the chest X-ray group over an average of 6.5 years of follow-up in the trial (17.6 per 1,000 versus 20.7 per 1,000).

An additional finding, which was not the main endpoint of the trial’s design, showed that all-cause mortality (deaths due to any factor, including lung cancer) was 6.7 percent lower in those screened with low-dose helical CT relative to those screened with chest X-ray. This difference was largely due to the decrease in lung cancer mortality. If lung cancer deaths were excluded, the differences in all causes of mortality between low-dose helical CT and chest X-ray were not statistically significant.