Description of the Evidence
With completion of the NLST, there is now evidence that screening with LDCT can reduce lung cancer mortality risk in ever-smokers who have smoked 30 pack-years or more. The NLST included 33 centers across the United States. Eligible participants were between the ages of 55 years and 74 years at the time of randomization, had a history of at least 30 pack-years of cigarette smoking, and, if former smokers, had quit within the past 15 years. A total of 53,454 persons were enrolled; 26,722 persons were randomly assigned to screening with LDCT and 26,732 persons were randomly assigned to screening with chest x-ray. Any noncalcified nodule found on LDCT measuring at least 4 mm in any diameter and x-ray images with any noncalcified nodule or mass were classified as positive, although radiologists had the option of not calling a final screen positive if a noncalcified nodule had been stable on the three screening exams. The LDCT group had a substantially higher rate of positive screening tests than did the radiography group (round 1, 27.3% vs. 9.2%; round 2, 27.9% vs. 6.2%; and round 3, 16.8% vs. 5.0%). Overall, 39.1% of participants in the LDCT group and 16.0% in the radiography group had at least one positive screening result. Of those who screened positive, the false-positive rate was 96.4% in the LDCT group and 94.5% in the chest radiography group. This was consistent across all three rounds.
In the LDCT group, 649 cancers were diagnosed after a positive screening test, 44 after a negative screening test, and 367 among participants who either missed the screening or received the diagnosis after the completion of the screening phase. In the radiography group, 279 cancers were diagnosed after a positive screening test, 137 after a negative screening test, and 525 among participants who either missed the screening or received the diagnosis after the completion of the screening phase. A total of 356 and 443 deaths from lung cancer occurred in the LDCT and chest x-ray groups, respectively, with a relative reduction in the rate of death from lung cancer of 20.0% (95% CI, 6.8–26.7) with LDCT screening. Overall mortality was reduced by 6.7% (95% CI, 1.2–13.6). The number needed to screen with low-dose CT to prevent one death from lung cancer was 320.