The purpose of the National Lung Screening Trial (NLST) was to evaluate the effect on both all-cause and lung cancer-related mortality from the use of low-dose computed tomographic (CT) screening in a population at high risk for lung cancer, using chest radiography as a comparison.
The trial involved 33 health care institutions across the United States and enrolled a total of 53,454 adults, 55 to 74 years of age, over 20 months. Of the enrollees, 26,722 were randomly assigned to undergo low-dose CT scanning and 26,732 to undergo chest radiography. Lung cancer screening occurred annually for three years (noted as T0, T1, and T2). Study participants completed questionnaires either annually or semiannually, and the National Death Index was consulted to collect outcome information. The median follow-up time was 6.5 years.
The low-dose CT screening method revealed significantly more positive test results at all three annual screenings, compared with chest radiography (T0, 27.3% versus 9.2%; T1, 27.9% versus 6.2%; T2, 16.8% versus 5.0%). Of the positive results, 96.4% in the low-dose CT group proved to be false positives, compared with 94.5% in the radiography group.
Overall, however, low-dose CT scanning detected 1,060 cancers during the study (645 cases per 100,000 person-years), compared with 941 cancers in the chest radiography group (572 cases per 100,000 person-years). Early-stage cancers (IA and IB) were most commonly diagnosed in both groups after a positive screening. There were 357 deaths from lung cancer in the low-dose CT arm (247 per 100,000 person-years) and 443 in the chest radiography arm (309 per 100,000 person-years), representing a 20% relative reduction in mortality from lung cancer. Deaths from any cause were also lower (by 6.7%) in the low-dose CT group than in the chest radiography group (1,877 versus 2,000, respectively).
Although the results seem to favor low-dose CT screening, the authors recommend that the high rate of false positives, its costliness, and potential for overdiagnosis be robustly evaluated before there is widespread adoption of this method.-AK
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