H. Gilbert Welch, M.D. and William Black, M.D., of the Dept. of Veterans Affairs Medical Center, White River Junction, Vt. and the Dartmouth-Hitchcock Medical Center used data from large randomized screening trials to estimate the extent of overdiagnosis. They found that about 25% of breast cancers detected on mammograms and about 60% of prostate cancers detected with prostate-specific antigen (PSA) tests could represent overdiagnosis. In a lung cancer screening trial of chest x-rays and sputum tests, they estimate that 50% of the cancers detected represented overdiagnosis. They argue that this estimate will only increase with spiral CT scanning, which, in one observational study, found almost as many lung cancers in non-smokers as smokers.The authors also point to cancer incidence and mortality statistics as evidence of overdiagnosis in some cancers. For five cancers—thyroid, prostate, kidney and breast cancer, and melanoma—data from the past 30 years show an increasing number of new cases but not an increase in deaths. In each of these cancers, an increase in screening or imaging tests has been associated with an increasing rate of new diagnoses.
The screening industry will not melt away since it drives traffic and dollars to high margin medical activities. It also has zealous supporters within the patient communities. Despite Dr. Welch's fervent and persistent cries, no amount of statistical data will sway the physician and patient zealots. Some day there will be a tally of the costs of over diagnosis and over treatment. Risk assessment will move beyond the paraffin, textiles dyes, and light microscopy and the label of cancer will be restricted to diseases that actually have malignant behavior. I am not sure when that will happen.