Overdiagnosis: An underrecognized cause of confusion and harm in cancer screening.

The Mayo Lung Project (MLP) was a National Cancer Institute-funded randomized clinical trial designed to determine the effectiveness of intensive screening with chest radiography and sputum cytology in comparison with usual care (1). The trial was begun in 1971 and was completed in 1983, when the average follow-up after the last screen was about 3 years. Although the 5-year survival for lung cancer was much higher in the screened group than in the control group, there was no difference in lung cancer mortality. This apparent discrepancy between survival and mortality along with an excess of 46 lung cancer cases in the screened group (206, as compared with 160 in the usual-care arm) has been the source of much controversy. Marcus et al. (2), in an attempt to resolve this controversy, used the National Death Index–Plus search to extend the follow-up of the MLP participants through 1996. The investigators report their findings in this issue of the Journal (2).