Overdiagnosis concerns raised for CT lung cancer screening

By Lynda Williams, Senior medwireNews Reporter

People participating in any future computed tomography lung cancer screening program would face a significant risk for overdiagnosis, US researchers caution in JAMA Internal Medicine.

Using data from the National Lung Screening Trial (NLST), the team calculated that 18.5% of the 1089 lung cancers detected over a 6-year period using low-dose computed tomography (LDCT) were likely to have been indolent and therefore overdiagnosed.

The probability of overdiagnosis rose to 22.5% for non-small-cell lung cancers and 78.9% for bronchioalveolar lung cancers detected by LDCT during the study, say Edward Patz Jr (Duke University Medical Center, Durham, North Carolina) and co-authors.

“In the new International Association for the Study of Lung Cancer histologic classification of adenocarcinomas, many of these tumors would be designated as minimally invasive adenocarcinomas, suggesting an indolent behavior and good long term outcome,” the team comments.

“These data raise the question as to the necessity and type of therapy required if a diagnosis of minimally invasive adenocarcinoma is established and challenge the diagnostic community to develop a classification scheme that could accurately phenotype all lung tumors.”

In addition, NLST findings indicated that 320 patients would need to be screened to prevent one patient dying from lung cancer, but the current study suggests that 1.38 patients would be overdiagnosed in this scenario.

“Whereas the NLST demonstrated a relative mortality reduction with LDCT, the limitations of the screening process, including the magnitude of overdiagnosis, should be considered when guidelines for mass screening programs are constructed,” Patz Jr et al write.

“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 NLST screened 53,452 individuals aged 55 to 74 years with a high risk for lung cancer, due to a history of smoking, between 2002 and 2004 and followed-up the cohort for over 6 years. Screening consisted of three annual LDCT or chest radiography studies, the researchers explain. LDCT screening was reported to have reduced lung cancer mortality by 20%.

Overdiagnosis – the likelihood that the lung cancer would not otherwise have become clinically apparent during the screening phase of the trial – was calculated from the excess number of lung cancers detected in the NLST using LDCT compared with those identified using chest radiography.

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