Low-Dose CT Screening Identifies More Early Lung Cancer But Has Lower Positive Predictive Value vs Radiography
Results of the two rounds of annual incidence screening with low-dose computed tomography (CT) vs radiography in the National Lung Screening Trial (NLST) were recently reported by Denise R. Aberle, MD, of University of California at Los Angeles, and colleagues in The New England Journal of Medicine. Among the findings of the trial is that low-dose CT was more sensitive in detecting early-stage lung cancers but had a lower positive predictive value compared with radiography.
The NLST was conducted to determine whether three annual screenings (prevalence round T0 and incidence rounds T1 and T2) with low-dose helical CT can reduce mortality from lung cancer compared with chest radiography in an asymptomatic high-risk population. The current analysis involved findings from the first two incidence screenings (rounds T1 and T2).
T1 Screening Round Results
At the T1 round, 24,715 (94%) of 26,285 eligible participants underwent CT screening, with positive results found in 27.9%. Of 26,410 eligible for radiography screening, 24,089 (91%) were screened, with positive results in 6.2%.
In the CT group, 186 participants were diagnosed with lung cancer, including 168 of 6,901 participants with positive screening results, 10 of 17,814 with negative screening results, 6 of 1,570 who were not screened at T1, and 2 of 437 ineligible participants with lung cancers that were first diagnosed during the T1 screening year.
In the radiography group, 133 participants were diagnosed with lung cancer, including 65 of 1,482 with positive screening results, 44 of 22,607 with negative screening results, 21 of 2,321 who were not screened, and 3 of 322 ineligible participants with lung cancers diagnosed during the T1 screening year.
For the CT vs radiography groups, sensitivity was 94.4% vs 59.6%, specificity was 72.6% vs 94.1%, positive predictive value was 2.4% vs 4.4%, and negative predictive value was 99.9% vs 99.8%.
T2 Screening Round Results
At the T2 round, 24,102 (93%) of 25,492 eligible participants underwent CT screening, with positive results found in 16.8%. Of 26,110 eligible for radiography screening, 23,346 (89%) underwent screening and positive results were found in 5.0%.
In the CT group, 237 participants were diagnosed with cancer, including 211 of 4,054 with positive screening results, 16 of 20,048 with negative screening results, 7 of 1,840 who were not screened at T2, and 3 of 780 ineligible participants with lung cancers diagnosed during the T2 screening year.
In the radiography group, 144 participants received a diagnosis of lung cancer, including 78 of 1,174 with positive screening results, 44 of 22,172 with negative screening results, 18 of 2,764 who were not screened, and 4 of 622 participants who were ineligible for the T2 screening but received a diagnosis of lung cancer during the T2 screening year.
For the CT vs radiography groups, sensitivity was 93.0% vs 63.9%, specificity was 83.9% vs 95.3%, positive predictive value was 5.2% vs 6.7%, and negative predictive value was 99.9% vs 99.8%.
Stages of Identified Cancers
Among lung cancers of known stage at T1, 87 (47.5%) were stage IA and 57 (31.1%) were stage III or IV in the low-dose CT group, and 31 (23.5%) were stage IA and 78 (59.1%) were stage III or IV in the radiography group. The differences in stage distribution between groups persisted at T2.
The increase in early-stage lung cancers in the CT group was associated with a decrease in late-stage lung cancers. Over the course of the trial, the incidence of stage IV lung cancer was 138 cases per 100,000 person-years in the CT group vs 204/100,000 person-years in the radiography group (rate ratio = 0.68, 95% confidence interval = 0.57–0.80).
The investigators concluded: “Low-dose CT was more sensitive in detecting early-stage lung cancers, but its measured positive predictive value was lower than that of radiography. As compared with radiography, the two annual incidence screenings with low-dose CT resulted in a decrease in the number of advanced-stage cancers diagnosed and an increase in the number of early-stage lung cancers diagnosed.”
The study was funded by the National Cancer Institute.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
