The blood test mostly commonly used to screen men for prostate cancer should be dropped, because it can result in  more harm than good, says a Canadian task force.

The prostate-specific antigen, or PSA, test measures inflammation that can be elevated for many reasons other than cancer, such as normal enlargement of the prostate with age or an infection.

Researchers said over-diagnosis occurs when cancer is detected correctly but would not cause symptoms or death.

The main problems are false-positive results and over-diagnosis, the review indicated. A positive PSA test result often leads to more tests such as a biopsy, which carries risks of bleeding, infection, and urinary incontinence.

In most men with prostate cancer, the tumour grows slowly, and they’re likely to die of another cause before the prostate tumour causes any symptoms.  

Prostate cancer is the most commonly diagnosed non-skin cancer in men. The prognosis for most prostate cancers is good, with a 10-year survival rate of 95 per cent.

Screening aims to find cancer before symptoms appear and reduce the chance of dying from cancer with early treatment.

In Monday’s issue of the Canadian Medical Association Journal, the Canadian Task Force on Preventive Health Care reviewed the latest evidence and international best practice to weigh the benefits and harms of PSA screening with or without digital rectal exams.

"Available evidence does not conclusively show that PSA screening will reduce prostate cancer mortality, but it clearly shows an elevated risk of harm. The task force recommends that the PSA test should not be used to screen for prostate cancer," Dr. Neil Bell, chair of the prostate cancer guideline working group member, and his team concluded.

The guideline is aimed at physicians and other health-care professionals and policymakers. It updates the task force’s recommendation from 1994 on screening with the PSA test.

The new recommendations include:

  • For men under age 55 and over age 70, the task force recommends not using the PSA test to screen for prostate cancer. This strong recommendation is based on the lack of clear evidence that screening with the PSA test reduces mortality and on the evidence of increased risk of harm.
  • For men aged 55–69 years, the task force also recommends not screening, although it recognizes that some men may place high value on the small potential reduction in the risk of death and suggests that physicians should discuss the benefits and harms with these patients.
  • These recommendations apply to men considered high risk — black men and those with a family history of prostate cancer — because the evidence does not indicate that the benefits and harms of screening are different for this group.

The key evidence was from a well-done European study. It showed inconsistent results, with a small potential positive effect over a long period of time, which the reviewers balanced against the clear evidence of harm, said Dr. James Dickinson, a member of the prostate cancer guideline working group and a professor of family medicine at the University of Calgary.

"Fundamentally this is not a good enough test to be worth using," Dickinson said in an interview. "Let's hope that better things come in the future, but right now it's not worth using. It's more likely to cause harm than benefit."

Watchful waiting advocated

A Canadian specialist, however, takes issue with the recommendation.

The task force’s guidelines are flawed for Canada, said Dr. Neil Fleshner, who studies and treats prostate cancer at Princess Margaret Cancer Centre in Toronto.

"By using the PSA test, we can absolutely find lethal cancers early and by intervening in those men, we can save their lives. Therefore, these recommendations undoubtedly will lead to more prostate cancer deaths," Fleshner said.

The task force's Bell said almost one in five men aged 55 to 69 have at least one false-positive PSA test, and about 17 per cent end up with unnecessary biopsies.

"If you screen men [aged 55 to 69] based on the protocol in those trials, every two to four years for 13 years, five out of 1,000 will die from prostate cancer. If you don't screen, six out of 1,000 men will die from prostate cancer," Bell said. "So the reduction in prostate cancer mortality is one in 1,000 or about 0.1 per cent."

"To get the benefit, you're diagnosing about 27 or 28 men with prostate cancer who would never benefit from the treatment related to prostate cancer because they would never suffer any difficulty from it."

Bell added that more than half of detected prostate cancers are over-diagnosed.

The task force said that separating screening from treatment through watchful waiting or active surveillance, could change the ratio of risks to benefits of PSA screening, but the hypothesis needs to be tested.

Dr. Murray Krahn of Toronto's University Health Network wrote a journal commentary on prostate cancer screening. 

Krahn said the task force guideline provides a good summary, but he would like to see more emphasis on patient preference, such as whether the harms are important, and shared decision-making.

On the sidelines of a recreational hockey game in Toronto, Rakesh Patel, 53, said he had a PSA test at his doctor's suggestion.

"She goes through the whole series of things that I should be aware of, especially at my age," Patel said.

The task force said it did not consider the costs of screening or treatment of prostate cancer.

With files from CBC's Kas Roussy and The Canadian Press