Background: A troubling aspect of cancer screening is the potential for overdiagnosis, i.e., detection of disease that, in the absence of screening, would never have been diagnosed. Overdiagnosis is of particular concern in lung cancer screening because newer screening modalities can identify small nodules of unknown clinical significance. Previously published analyses of data from the Mayo Lung Project, a large randomized controlled trial conducted among 9211 male cigarette smokers in the 1970s and early 1980s indicated that overdiagnosis might exist in lung cancer screening. At the end of follow-up (July 1, 1983), no difference in lung cancer mortality was observed, but an excess of 46 cases in the intervention arm suggested overdiagnosis. Because that excess could instead have resulted from short follow-up time, we investigated this possibility by conducting long-term lung cancer incidence follow-up.

Methods: We investigated the lung cancer status through 1999 of the 7118 participants in the Mayo Lung Project who were alive and without diagnosed lung cancer in 1983 by use of medical records, surveys mailed to participants or next-of-kin, and state death certificates.

Results: Information was available for 6101 participants, including 811 with inconclusive lung cancer status. From November 1971 through December 31, 1999, 585 participants in the intervention arm and 500 in the usual-care arm were diagnosed with lung cancer.

Conclusions: The persistence of excess cases in the intervention arm after 16 additional years of follow-up provides continued support for overdiagnosis in lung cancer screening.