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.