An estimated 18% of the early lung cancers detected by low-dose CT screening in the National Lung Screening Trial were likely indolent and probably represent overdiagnosis, according to a report published online Dec. 9 in JAMA Internal Medicine.
The National Lung Screening Trial (NLST) found "an encouraging" 20% relative reduction in lung cancer–specific mortality among high-risk patients who were screened using low-dose CT, compared with chest radiography. "These findings were met with enthusiasm, but before a widespread public health screening program is implemented, risks of screening also need to be considered," said Dr. Edward F. Patz Jr. of the department of radiology, Duke University Medical Center, Durham, N.C., and his associates in the NLST.
The chief risk in this case is overdiagnosis: identifying an early-stage lesion in an asymptomatic patient that would not progress or affect that patient’s long-term health. It is likely that some of the tumors detected on low-dose CT were just such indolent cancers, and that those patients unnecessarily underwent invasive diagnostic procedures, surgical resection, and multiple follow-up studies.
To estimate how many of the detected cancers in the NLST were indolent – and thus overdiagnosed – Dr. Patz and his colleagues used statistical probability methods to analyze extended follow-up data from the study.
The NLST involved 53,452 men and women aged 55-74 years who were enrolled during 2002-2004 and who had at least a 30-pack-year history of cigarette smoking. The patients were randomly assigned to undergo lung cancer screening using either three annual low-dose CT exams or three annual single-view chest radiographs.
Mean follow-up was approximately 6 years. "At the end of the entire trial, there were 1,089 total lung cancer cases in the low-dose CT arm (649 detected by low-dose CT screening) and 969 cases in the [radiology] arm, for an excess of 120 cases. This gives [an] excess cancer rate of 18.5%," the investigators said (JAMA Intern. Med. 2013 Dec. 9 [doi:10.1001/jamainternmed.2013.12738]).
"The data from this study suggest that ... 18% of persons in the low-dose CT arm with screen-detected lung cancer and 22% of those in the low-dose CT arm with screen-detected NSCLC [non–small cell lung cancer] may be cases of overdiagnosis," Dr. Patz and his associates said. "In other words, if these individuals had not entered the NLST, they would not have received a lung cancer diagnosis or treatment, at least for the next 5 years."
In the future, the study authors noted, "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 National Institutes of Health supported the NSLT. No financial conflicts of interest were reported.