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Prostate cancer screening under scrutiny

There is insufficient evidence to support population-wide screening for prostate cancer using the prostate specific antigen (PSA) test, conclude two papers published on today.

The authors say that the PSA test cannot distinguish between lethal and harmless prostate cancer, leading to overdiagnosis and overtreatment of healthy men.

PSA is a protein produced in the cells of the prostate gland. It is present in small quantities in the blood of healthy men, and is often elevated in men with prostate cancer and in men with benign prostatic enlargement.

PSA screening is widely used in many countries, but it remains controversial. A recent study showed that prostate cancer deaths were lower among screened men but at a cost of considerable overdiagnosis and treatment.

So in the first study, a Swedish team of researchers set out to assess how well prostate specific antigen predicted a future prostate cancer diagnosis.

Using PSA test results from 540 men diagnosed with prostate cancer measured several years before diagnosis and from 1,034 healthy controls, they found that the PSA test did not attain the likelihood ratios (a measure used to predict disease) required for a screening test. Only very low concentrations of PSA, less than 1ng/ml, virtually ruled out a diagnosis of prostate cancer during follow-up.

The authors conclude that additional biomarkers for early detection of prostate cancer are needed before population based screening for prostate cancer should be introduced.

In a second analysis paper, US researchers reviewed the benefits and harms of PSA screening and conclude that data on costs and benefits remain insufficient to support population based screening. They also say that the financial and psychological costs of false positive results, overdiagnosis and overtreatment of prostate cancer need to be measured more precisely.

Finally, they believe that men should be fully informed of the benefits, risks and uncertainty associated with the PSA test before they are screened.

This view is supported in an accompanying editorial by researchers at Monash University in Australia.

Clinicians and patients are faced with many uncertainties when considering whether or not to undergo prostate screening, write Dr Dragan Ilic and Professor Sally Green.

Further research is required to develop and evaluate a valid screening test for prostate cancer, they say. Until such a test is available, a shared decision making approach to undertaking screening should be adopted.