A study by U.S. academics shows that annual CT screening in older smokers or those with a history of heavy smoking can reduce associated mortality. The first round of screening results from the National Lung Cancer Screening Trial (NLST) showed that annual low-dose spiral CT detected significantly more early-stage lung cancers than conventional chest X-rays over three years, according to the researchers. The paper was published online May 23, 2013, in the New England Journal of Medicine. A total of 53,454 asymptomatic men and women aged 55 to 74 years were enrolled in the first screening round of the study. All subjects had a history of smoking of at least 30 packs/year and had smoked or quit smoking for less than 15 years currently. Subjects were recruited from 33 hospitals across the United States and were randomized to receive either low-dose spiral CT (n=26,722) or chest x-ray (n=26,732) to screen for lung cancer on an annual basis for 3 years. Eight subjects who were found to have lung cancer prior to the first screening were excluded from this study. The results showed that the percentage of subjects with positive screening results was 27.3% in the low-dose CT scan group, which was significantly higher than the 9.2% in the chest X-ray group. The percentage of subjects diagnosed with lung cancer was 1.1% and 0.7% in the two groups, respectively. In the CT group, 92.5% of subjects who developed lung cancer had a positive screening result (true positive result), 6.2% had a negative screening result (false negative result), and the remaining patients did not receive a scheduled screening visit. In the chest X-ray examination group, 71.6 percent of subjects who developed lung cancer had a true-positive screening result, 25.8 percent had a false-negative result, and the remaining patients did not receive a scheduled screening visit. The sensitivity and specificity of lung CT were 93.8 percent and 73.4 percent, respectively, compared with 73.5 percent and 91.3 percent for chest X-rays, the researchers added. More fine bronchoalveolar carcinomas (8 vs. 38 cases) and adenocarcinomas (71 vs. 123 cases) occurred in the low-dose CT scan group compared with the chest X-ray examination group, but both groups were similar in terms of other histological features. The difference between the two groups in terms of the number of cancers detected was almost entirely caused by the fact that CT screening was significantly more likely to detect early stage tumors (stage IA). In contrast, for more advanced malignancies, the detection rate of CT screening was very similar to that of chest radiography.