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Low-dose CT scan may predict early-stage lung cancer
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Two low-dose CT screenings may effectively detect early-stage lung cancer, results from the National Lung Screening Trial suggest.
Researchers conducted the trial to determine how effectively two regimens — three annual screenings with low-dose helical CT or chest radiography — reduced lung cancer mortality.
The analysis included details of the first two CT incidence screenings. The investigators evaluated adherence to screening protocols, the results of screening and downstream diagnostic tests, and characteristics of lung cancer cases.
During the first round of tests, researchers reported positive results in 27.9% of those who underwent low-dose CT and 6.2% of those who underwent radiography. During the second round, rates of positive results were 16.8% in the low-dose CT group and 5% in the radiography group.
At the first test point, low-dose CT yielded a 94.4% sensitivity and a 72.6% specificity, for a positive predictive value of 2.4% and a negative predictive value of 99.9%. At the second testing point, the positive predictive value increased to 5.2%, according to researchers.
Radiography yielded a 59.6% sensitivity and a 94.1% specificity at the first test point, for a positive predictive value of 4.4% and a negative predictive value of 99.8%. Sensitivity and positive predictive value both increased at the second test point.
In the low-dose CT group, 47.5% of cancers were stage IA and 31.1% were stage III or IV at the first testing point. In the radiography group, 23.5% were stage IA and 59.1% were stage III or IV at the first time point. These proportional differences persisted through the second time point.
The researchers concluded that low-dose CT may be a more sensitive tool for detecting early-stage disease, but that radiography was associated with a higher positive predictive value.
“The two incidence screenings in the National Lung Screening Trial provide evidence that, in a high-risk cohort, annual screening with low-dose CT detects more lung cancers than radiography and results in a stage shift toward early-stage, non–small cell lung cancers, which are potentially curable,” the researchers wrote. “The performance characteristics of low-dose CT may be enhanced by determining the most appropriate risk cohort, refining both algorithms for interpreting the results of screening and definitions of positive findings, and determining the appropriate duration and timing of screening.”
Disclosure: The study was funded by the NCI.
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Hongbin Chen, MD, PhD
The National Lung Screening Trial reported a 20% relative reduction in mortality from lung cancer with three rounds of low-dose CT screening as compared with radiography. This paper provides more detailed information from the two incidence screenings (rounds T1 and T2). It confirms that the benefits of low-dose CT screening resulted from higher sensitivity to detect lung cancers — especially early-stage non–small cell lung cancer, in which treatment is more effective.
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