Many cancers detected by screening tests are not destined to cause symptoms or death and therefore represent a phenomenon known as overdiagnosis. And because overdiagnosis leads to unnecessary treatment and other harms, it is important to develop clinical and research strategies to quantify, recognize, and manage it, according to a review published online April 22 in the Journal of the National Cancer Institute.
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 cancersthyroid, prostate, kidney and breast cancer, and melanomadata 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.
In addition to screening, other procedures, such as diagnostic imaging, may contribute to overdiagnosis. CT colonography (virtual colonoscopy) for instance, often detects abnormalities outside the colon that can lead to more tests and possibly overdiagnosis.
The authors suggest several strategies to address the problem. One is to educate patients about the risks a
|Contact: Caroline McNeil|
Journal of the National Cancer Institute