Some Lung Cancers Detected by Low-Dose CT in National Lung Screening Trial May Be Indolent

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More than 18% of all lung cancers detected by low-dose computed tomography in the National Lung Screening Trial (NLST) may be clinically insignificant. Overdiagnosis should be considered when describing the risks of [low-dose computed tomography] screening for lung cancer, according to a review of extended follow-up data from the NLST. The results were published in JAMA Internal Medicine by a team of investigators led by Edward F. Patz, Jr, MD, of Duke University Medical Center in Durham, North Carolina.

The NLST compared screening with low-dose computed tomography vs chest radiography among 53,452 persons at high risk for lung cancer who were observed for 6.4 years. “During follow-up, 1,089 lung cancers were reported in the [low-dose computed tomography] arm and 969 in the [chest radiography] arm of the NLST,” the investigators reported. They determined that the probability was 18.5% (95% confidence interval [CI] = 5.4%–30.6%) that any lung cancer detected by screening with low-dose computed tomography was an overdiagnosis, 22.5% (95% CI = 9.7%–34.3%) that a non–small cell lung cancer detected by low-dose computed tomography was an overdiagnosis, and 78.9% (95%CI = 62.2%–93.5%) that a bronchioalveolar lung cancer detected by low-dose computed tomography was an overdiagnosis.

Study Methodology

Those participating in the NLST had at least a 30 pack-year history of cigarette smoking and were between the ages of 55 and 74 when enrolled. Subjects were randomly assigned to receive either three annual low-dose computed tomography studies (n = 26,722) or three annual single-view posterior-anterior chest x-rays (n = 26,730) and then observed for up to 5 more years. Low-dose computed tomography “demonstrated an encouraging 20% relative reduction in lung cancer–specific mortality compared with screening using chest radiography,” the researchers commented.

Findings from the NLST “were met with enthusiasm, but before a widespread public health screening program is implemented, risks of screening also need to be considered,” the authors wrote. Their analyses “were performed to provide an empirical estimate of, or at least an upper bound on, the magnitude of overdiagnosis in the NLST so that the impact on mass screening programs could be understood.”

The magnitude of overdiagnosis “should be considered when guidelines for mass screening programs are constructed,” the researchers stated. “In the future, once there are better biomarkers and imaging techniques to predict which individuals with a diagnosis of lung cancer will have more or less aggressive disease, treatment options can be optimized, and a mass screening program can become more valuable,” the authors concluded. ■

Patz EF Jr, et al: JAMA Intern Med. December 9, 2013 (early release online).




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