Screening may lead to overdiagnosis of lung cancer, a study reports in the June 7 issue of the Journal of the National Cancer Institute.

Screening for cancer can find tumors that might not otherwise have been diagnosed in a person's lifetime, a situation called overdiagnosis. Overdiagnosis wastes health care resources. Tests and treatment resulting from overdiagnosis can lead to substantial toxicity and even premature death in patients.

Pamela M. Marcus, Ph.D., of the National Cancer Institute in Bethesda, Md., and colleagues surveyed 7,118 participants in the Mayo Lung Project for information on their lung cancer diagnosis, health, and smoking history, and chest scan results after the study's initial follow-up in July 1983. The patients in the initial project had been randomly placed in two groups, one of which underwent multiple screening chest x-rays and spectrum tests used to identify lung cancer.

The authors identified a total of 585 cancers in the patients in the screened arm and 500 cancers in the group that was not screened. They report that the 85 more cancers found in screened patients suggests that screening can lead to lung cancer overdiagnosis.

"Although the magnitude of overdiagnosis in chest x-ray screening appears to be modest, the very real and deleterious role that overdiagnosis plays in mass screening can not be discounted. The newest imaging technologies can detect very small lung abnormalities, but these abnormalities may be clinically unimportant. The question remains as to whether early detection of lung cancer through mass screening results in a net benefit to the public's health." the authors write.

In an accompanying editorial, Edward F. Patz, Jr., M.D., of Duke University Medical Center in Durham, N.C., writes, "Instead of the theoretical convergence of the number of lung cancer cases in the screened and control groups, [the authors] found an increasing discrepancy between the two trial arms. The explanation for the increase is uncertain, although this compelling evidence supports the author's conclusion that overdiagnosis bias must be considered in lung cancer screening trials."

Ariel Whitworth
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Journal of the National Cancer Institute
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