Prostate cancer screening does not appear to significantly reduce the risk of death from the disease, a 20-year study suggests.

Prostate cancer screening is used worldwide but remains controversial. Critics say it leads to unnecessary biopsies and treatment with little proof of life-saving benefits.

The screening includes a rectal exam and a blood test, called PSA, that looks for high levels of prostate specific antigen.

A high PSA may signal cancer, but levels can also be above normal because of a benign enlargement of the prostate or inflammation. And the cancer itself may not be dangerous.

In Thursday's online issue of the British Medical Journal, Swedish researchers say they found only a modest difference in rates of deaths between 1,494 men who were randomly selected for screening every third year for 20 years and another 7,532 men who were not screened and acted as controls.

The men were 50 to 69 years old.

Eighty-five men in the screening group, or about six per cent, were diagnosed with prostate cancer during the study. In the control group, 292 men, or nearly four per cent, were diagnosed with the disease after they showed symptoms.

Radiation treatment is pinpointed on a prostate cancer patient. Before having a PSA, men with no symptoms should be informed about potential hazards of treatment, European researchers say. Paul O'Neill/East Valley Tribune/Associated Press

"After 20 years of followup, the rate of death from prostate cancer did not differ significantly between men in the screening group and those in the control group," Gabriel Sandblom of the Karolinska Institute in Sweden and colleagues concluded.

Large studies in both the U.S. and Europe also found little or no benefit from screening, although the U.S. study may have been too short to offer reliable data on mortality, Sandblom's team said.

The authors suggested that before having a PSA, men with no symptoms should be informed about potential hazards of treatment after a result points to cancer. They include erectile dysfunction, urinary incontinence and bowel symptoms.

"There is no escaping the fact that we need a better tool … to help detect prostate cancers that actually need treating, as opposed to innocent ones that do not," agreed Malcolm Mason, a prostate cancer expert at Cancer Research U.K.

"In the meantime, men should be fully informed about the pros and cons of having their PSA measured."

The next goal for prostate screening should be to determine which cancers detected are harmless and which are high risk and need treatment, the Swedish scientists said.

About 25,000 Canadian men are diagnosed with prostate cancer each year and 4,300 die of it, according to the Canadian Cancer Society.

With files from The Associated Press