LDCT has been shown in recent clinical trials to be an effective screening tool in some patients, but some of the tumors it finds may be indolent (slow growing) or clinically insignificant. Overdiagnosis is the detection of a cancer with a screening test that wouldn't otherwise have become clinically apparent. It is a potential harm of screening because of the additional cost, anxiety and complications associated with unnecessary treatment, according to the study background.

Edward F. Patz Jr., M.D., of Duke University Medical Center, Durham, N.C., and colleagues examined data from the National Lung Screening Trial, which compared LDCT screening vs. chest radiography (CXR) among 53,452 people at high risk for lung cancer, to estimate overdiagnosis.

Among 1,089 lung cancers reported in the LDCT group during follow-up, the authors estimated that 18.5 percent represented an overdiagnosis. They also estimated that 22.5 percent of non-small cell lung cancer detected by LDCT represented an overdiagnosis, and that 78.9 percent of bronchioalveolar (air sacs) lung cancers detected by LDCT represented an overdiagnosis.

"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 conclude.