A national task force that issues guidelines for doctors says PSA testing should not be used to screen men for possible prostate cancer because it can lead to more harms than benefit.

The Canadian Task Force on Preventive Health Care says measuring prostate specific antigen, or PSA, in blood is not an effective screening tool because it often produces false-positive results that lead to unnecessary treatment.

Task force member Dr. Neil Bell says almost one in five men aged 55 to 69, for instance, have at least one false-positive PSA test and about 17 per cent end up with unnecessary biopsies.

Bell says more than half of detected prostate cancers are overdiagnosed — meaning they would not have caused symptoms or death during a man’s lifetime.

Overdiagnosis often leads to treatments that can cause impotence, incontinence and infection. But Bell says PSA screening results in only a 0.1 per cent reduction in prostate cancer deaths — or one less death per 1,000 men.

The task force recommendation applies only to using PSA testing to see if a man might have prostate cancer, not for checking whether treatment is working in men already diagnosed with the disease.

“Our recommendation is against screening because we think the harms are sufficiently great . . . (and) the majority of men would probably not benefit from that process,” Bell said of PSA screening, which is often done every two to four years starting at about 40.

“That being said, men who are concerned about prostate screening should have a discussion with their physician . . . to come up with the decision that’s appropriate for that person.”

“Physicians and patients need to be aware of the fact that in prostate cancer, early diagnosis doesn’t always mean you’re going to get a better benefit.”

The guidelines are published in Monday’s edition of the Canadian Medical Association Journal.