Lung Cancer Screening With CT Leads to Overdiagnosis

Low-dose computed tomography (LDCT) results in an approximately 18% overdiagnosis of lung cancer. The overdiagnosis reflects detection of indolent cancers.

Edward F. Patz, MD, from Duke University Medical Center in Durham, North Carolina, and colleagues published their analysis of data from the National Lung Screening Trial (NLST) online December 9 in JAMA Internal Medicine. The NLST compared LDCT screening with chest radiography (CXR) screening in individuals at high risk for lung cancer.

The original analysis of the NLST data revealed that screening for lung cancer with LDCT resulted in a 20% relative reduction in mortality.. The analysis also revealed the problem of overdiagnosis. Overdiagnosis is a potential harm because of additional cost, anxiety, and complications associated with unnecessary treatment.

The current analysis was performed to determine the magnitude of overdiagnosis in the NLST group relative to the CXR group. Dr. Patz and colleagues examined data for 53,452 individuals who were screened for an average of 6.4 years. The LDCT group included 1089 reports of lung cancer, and the CXR group included 969 reports of lung cancer.

The analysis indicates a probability of 18.5% (95% confidence interval [CI], 5.4% - 30.6%) that any lung cancer detected in the LDCT group was an overdiagnosis. Individuals given a diagnosis of nonsmall-cell-lung cancer (NSCLC) by LDCT had a 22.5% (95% CI, 9.7% - 34.3%) probability of overdiagnosis.

The authors suggest that the issue of overdiagnosis be seriously considered when constructing guidelines for mass screening programs.

"The true extent of overdiagnosis in lung cancer is difficult to determine because most of what we know about this disease is derived from symptomatic patients," the authors write.

They attempt to explore the overdiagnosis further by using a convolution model to examine the effect of other screening scenarios on overdiagnosis. The model was based on 3 annual screens for a total of 7 years of follow-up.

"Using the model, we found that the excess cancer rate associated with 3 annual LDCT screens decreased substantially in changing from the NLST follow-up (approximately 5 years after screening) to lifetime follow-up, with the latter estimates representing true overdiagnosis," the authors explain.

This research was supported by the National Institutes of Health. The authors have disclosed no relevant financial relationships.

JAMA Intern Med. Published online December 9, 2013.

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