Low-Dose CT versus Chest Radiography for Lung Cancer Screening

It is estimated that lung cancer, the largest single cause of cancer death in the world, will account for >100,000 deaths in the United States in 2013. The majority of patients with lung cancer have been smokers and half of the 94 million US smokers or former smokers remain at risk decades following smoking cessation.

The National Lung Screening Trial (NLST) screened for lung cancer in elderly persons who were heavy smokers. Among the NLST cohort, mortality from lung cancer was lower with the use of 3 years of annual screening with low-dose helical computer tomography (CT) than with the use of chest radiography.

Results from the initial round of screening, diagnosis, and treatment in the NLST were reported recently in the New England Journal of Medicine [2013;368(21):1980-1991].

Eligible participants had a history of at least 30 pack-years of smoking and were either current smokers or had been smokers within the previous 15 years. They were randomly assigned to undergo annual screening with the use of either low-dose CT or chest radiography for 3 years. Positive results were defined as nodules or other suspicious findings.

A total of 53,454 asymptomatic participants 55 to 74 years of age were recruited from 33 centers in the United States from August 2002 through April 2004. Of those, 26,722 were assigned to low-dose CT and 26,732 were assigned to chest radiography. Eight participants had lung cancer and 7 died before the first screening, leaving 26,715 in the low-dose CT group and 26,724 in the chest radiography group.

The first scheduled screening was performed in 98.5% of those in the low-dose CT group (n=26,309) and in 97.4% of those in the chest radiography group (n=26,035). There were no significant differences in compliance between the 2 groups.

The proportion of participants with positive screening results was higher in the low-dose CT group (7191/26,309; 27.3%) compared with the chest radiography group (2387/26,035; 9.2%). In both groups, rates of positive results increased slightly with older age and a larger number of pack-years of smoking.

The proportion of all screened participants who had negative results, but potentially clinically significant, noncancerous abnormalities, was higher in the low-dose CT group compared with the chest radiography group (10.2% vs 3.0%).

Of the 9578 participants who had positive results, 98.1% (n=9397) had completely documented diagnostic follow-up: at least one diagnostic procedure was performed in 90.4% (n=6369/7049) of the low-dose CT group and 92.7% (n=2176/2438) of the chest radiography group.

Lung cancer was diagnosed in 292 participants in the low-dose CT group and 190 in the chest radiography group; the difference was nearly completely accounted for by the higher incidence of stage IA cancer in the low-dose CT group (132 cases vs 46 in the radiography group). There were no significant differences in the total number of lung cancers in stages IIB through IV between the 2 groups.

The researchers cited some limitations to the study: compared with the general US population, the study group had a higher proportion of former smokers and a higher education level, and limiting the count of the number of follow-up procedures to those in participants with positive screening results.

“The NLST initial screening results are consistent with the existing literature on screening by means of low-dose CT and chest radiography, suggesting that a reduction in mortality from lung cancer is achievable at US screening centers that have staff experiences in chest CT," the authors said.