The much-debated prostate-specific antigen (PSA) test used to assess patients’ risk of prostate cancer is receiving a big formal thumbs down from one major national organization, who views the test as highly inaccurate and susceptible to overdiagnosis.

Current Problems

A new study from the Canadian Task Force on Preventive Health Care argues PSA tests present patients with too many risks and not enough certainty to merit widespread clinical use. This is despite prostate cancer being one of the most common cancers among men in the United States. Researchers claim overdiagnosis could lead to unnecessary treatment, causing infection or reproductive complications.

“Some people believe men should be screened for prostate cancer with the PSA test, but the evidence indicates otherwise,” said Dr. Neil Bell, member of the Canadian Task Force on Preventive Health Care and lead author of the new recommendations, in a statement. Data indicate between 11.3 and 19.8 percent of men with prostate cancer diagnosed through PSA tests will receive a false-positive diagnosis. Forty to 56 percent will be affected by overdiagnosis, leading to invasive treatment.

As a blood test, the PSA test actually does a good job at detecting prostate cancer; the protein that acts as a biomarker tends to show up in greater amounts when cancer is present. The problem is that it detects other things, too. In rarer cases, it may also produce a false-negative — when the person really does have cancer but his test comes back negative. The upside is that prostate cancer is generally slow to progress and seldom results in death.

The new recommendations make some key distinctions depending on the patient. For people younger than 55 and older than 70, the researchers advise against the PSA test outright. They credit a lack of evidence that PSA tests reduce mortality and a wealth of evidence that the tests may increase harm. For men 55 to 69, the recommendations remain the same; however, men in this group face the greatest risks, so the researchers advise patients to have an honest discussion with their doctors on the risks and benefits first.

U.S. guidelines uphold the these recommendations. In 2012, the U.S. Preventive Services Task Force issued its own set of guidelines that found the false-positives that result from PSA tests can lead to fever, infection, bleeding, and pain, most often as a result of the biopsies that get drawn if a patient’s PSA levels are too high. Men may also suffer urinary incontinence or impotency as a result of the test.

However, not all experts are so quick to reject the PSA test. While the method isn’t as reliable as some experts would like, one factor Bell and his colleagues didn’t account for is overall cost. In a related commentary, Dr. Murray Krahn suggests the quality-of-life costs as well as financial costs could easily outpace the one-time costs of a PSA test, which has been shown effective in some cases. Patient preference is also a factor, Krahn argues. A rectal exam may be uncomfortable to some but impossible for others, specifically if they can't handle needles.

“The report does not include a comprehensive review of patient harms; yes, they happen,” he writes, “but are they important?” To Krahn, the PSA test’s supreme benefit is in its patient-friendliness. Unlike biopsies, which demand a dozen tiny samples from the prostate gland itself, the PSA needs only a blood draw. Oftentimes, however, a worrisome PSA test may lead to biopsies anyway.

Finding The New PSA

In reality, the debate over PSA tests may already be somewhat antiquated. Recent research has shown biomarkers are by no means the most effective indicators for cancer. In April, for instance, scientists from Eindhoven University of Technology, in the Netherlands, showed the same principles behind ultrasound imaging could be leveraged to look at a patient’s prostate. Instead of using blood tests as the middle man, doctors can look directly at the prostate and use an injectable contrasting agent to see the mismatched blood vessels that indicate cancerous tissue.

Or there was the September finding from doctors at the Guangdong Medical College in China of a non-invasive blood test that carries a 98.1-percent accuracy rating. The technique relies on two technologies: an existing imaging technique called surface-enhanced Raman scattering, which shines a light on the body’s cells, and a piece of equipment called a support vector machine that analyzes what the imaging picks up.

These techniques are still confined to the lab, unfortunately. In the meantime, Bell and his colleagues recommend patients talk to their doctors as frankly as possible. The PSA test may be effective at finding cancer, argues Dr. James Dickinson, member of the prostate cancer guideline working group, but it’s not perfect.

“Any use of PSA testing to screen for prostate cancer requires a thoughtful discussion between the clinician and the patient about the balance between unclear benefits and substantial harms,” he said.

Source: Bell N, Gorber S, Shane A, et al. Recommendations on screening for prostate cancer with the prostate-specific antigen test. CMAJ. 2014.