Early diagnosis might mean overdiagnosis for prostate cancer
MedWire News: Prostate cancer and other oncology patients must be adequately informed of the nature and magnitude of the trade-off involved with early cancer detection, say US researchers investigating the theory that early detection is always better.
The team estimates that 60% of prostate cancers detected by prostate-specific antigen (PSA) screening will not cause symptoms or death and therefore represent overdiagnosis.
“Although early diagnosis may offer the opportunity to reduce the risk for cancer death, it can also lead one to be diagnosed and treated for a ‘cancer’ that is not destined to cause problems,” write Gilbert Welch (Department of Veterans Affairs Medical Center, White River Junction, Vermont, USA) and William Black (Dartmouth–Hitchcock Medical Center, Lebanon, New Hampshire, USA).
The prerequisites for overdiagnosis, according to the researchers, are apposite for prostate cancer. These include a “disease reservoir of detectable cancers,” ie, the existence of sub-clinical cancers (estimated from autopsy studies to be present in 30–70% of men older than 60 years), and activities leading to early detection, ie, PSA screening.
Commenting on the research published in the Journal of the National Cancer Institute, editorialist Laura Esserman from the University of California San Francisco, USA, stressed that all diagnostic procedures have direct and indirect costs, and are associated with a risk for complications and negative emotional consequences.
Welch and Black evaluated the results of the European Study of Prostate Cancer trial in which prostate cancer incidence was compared between men who underwent screening and those who did not. An extra 34 prostate cancers were detected per 1000 men screened, arising from the 58 screen-detected cases per 1000 men overall. Welch and Black equate this excess to a 60% chance that PSA-detected cancers are over-diagnosed.
The authors also point to cancer incidence and mortality statistics as evidence of overdiagnosis. Surveillance Epidemiology and End Results data from 1975 to 2005 show a slight decline in prostate cancer deaths, which is likely attributable to a combination of increased screening activity and improved treatment. However, this is paralleled with a steep increase in prostate cancer diagnoses.
“We need to be more judicious about how we screen,” said Esserman.
“We must… redefine cancer using our biological understanding of this disease… we must be clearer about what it is we are seeking to detect… and we must work in multidisciplinary teams to test and improve our reporting and thresholds for intervention,” she concluded.
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By MedWire Reporters