PSA Screening: The Controversial Test for Prostate Cancer

Paul Han, MD, MA, MPH, is the Director of the Center for Outcomes Research and Evaluation at Maine Medical Center Research Institute. In June 2016, Maine Cancer Foundation awarded Maine Medical Center a $400,000 grant over four years for The Maine Lung Cancer Prevention and Screening (Maine LungCAPS) InitiativeMaine LungCAPS is a multi-institution, multi-disciplinary collaboration of Maine health care providers and stakeholders. Dr. Han serves as Principal Investigator for the initiative, designed to improve the prevention, early detection and treatment of lung cancer in Maine

The month of September is dedicated to men’s health and prostate cancer. In our guest blog series, Dr. Han shares his opinions about the prostate-specific antigen (PSA) test, a blood test used to screen for prostate cancer.

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Prostate cancer is the most common cancer and the third leading cause of cancer deaths among US men.  The prostate-specific antigen (PSA) test is a blood test used to “screen” for prostate cancer—that is, to detect cancer at an early stage, when it can be effectively treated.  PSA testing is currently the only available screening test for prostate cancer, and for many years it has been widely used. 

PSA screening has also been controversial.  It’s not a perfect test because it misses some cancers (leading to false reassurance), and can also produce false-positive results (“false alarms”), which can lead to unnecessary anxiety and prostate biopsy procedures.  And although prostate cancer can be aggressive and lethal, many of the cancers detected by the PSA test will never grow, spread, or cause additional problems. 

Since it’s hard to know whether any individual man’s cancer will be lethal or harmless, most men with prostate cancer detected by PSA screening undergo treatments including surgery or radiation therapy—even the men who don’t need to be treated.  Research shows that PSA screening has a relatively small benefit in reducing deaths from prostate cancer; for every 1000 men who have the PSA test, only about 1-2 men (0.1%-0.2%) will be prevented from dying of prostate cancer.  998 out of every 1000 men who have the PSA test will not benefit from it. But this lack of benefit is not the only problem; screened men who are diagnosed with prostate cancer can also suffer harms from treatment, including urinary incontinence and erectile dysfunction.

PSA screening poses a dilemma.  It’s an imperfect test for an often non-lethal disease, which leads to over-diagnosis and over-treatment of cancers that are not harmful, and it requires a large number of men to be screened in order to prevent a small number of deaths.  And yet, PSA screening is the best and only method we have to detect prostate cancer early. If you’ve ever known someone who has suffered or died from prostate cancer, you want to do something to catch it early.

Over the past several years, major professional organizations have offered differing views on the value of PSA screening.  In 2012, the US Preventive Services Task Force (USPSTF) evaluated the available scientific evidence and recommended against routine PSA screening.  However, in April 2017 the USPSTF conducted an updated evaluation and issued a revised draft recommendation that advocated considering PSA screening for men aged 55-69, through a process of “informed, individualized decision making based on a man’s values and preferences.”  The USPSTF made this change based on newer evidence on the benefits of PSA screening in reducing prostate cancer deaths and metastatic disease, along with the growing use of “active surveillance,” a conservative management strategy for early-stage prostate cancer. 

Active surveillance involves carefully watching for signs that a man’s cancer is beginning to spread, and only treating the cancer if spreading happens.  It is a promising strategy for treating prostate cancer because it can reduce over-treatment of cancers that are not destined to cause problems. The revised USPSTF recommendation statement was issued for public comment and has not yet been finalized, but will most likely be adopted. 

Last week, a new study was published adding support to the revised recommendation. An international team of researchers reanalyzed data from the two largest and most influential studies of PSA screening. Both studies aimed to compare whether men who were randomly assigned to receive PSA screening had fewer prostate cancer deaths than men who were assigned to no screening. In both studies, many men in the no screening group ended up receiving some screening, which made it hard to determine how helpful screening was. The researchers re-analyzed the data to account for the amount of screening each man received, and found that PSA screening led to a clear reduction in prostate cancer deaths.

These new findings support the potential value of PSA screening.  Accordingly, the new USPSTF recommendation urges clinicians not to take PSA screening “off the table,” but to inform individual men about the potential benefits and harms of screening, and to reach a shared decision about screening based on each man’s own personal values.  We know PSA screening saves lives, but the number of lives saved compared to the number of men who must be screened (and thus the benefit to any one man) remains small. Screening leads to over-diagnosis of many non-lethal prostate cancers along with over-treatment which harms many men for no reason.  Promising new strategies, like active surveillance and methods for estimating an individual man’s risk of poor outcomes, may reduce these harms.  But for now PSA screening presents a difficult dilemma for patients and clinicians. 

The remaining challenge is how to ensure informed and shared decision making about PSA screening.  The information a patient needs to make an informed decision is complex, and most busy clinicians find it challenging to discuss everything in a brief office visit.  Nevertheless, shared decision making remains very difficult to put into practice. I hope we will find innovative ways to empower men to make the best possible decisions about whether PSA screening is best for them.

Please note: Thoughts and opinions expressed in Maine Cancer Foundation's guest blog series are the views of the writers.

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Should You Be Screened? Here's a Helpful Infographic

 

 

Wednesday, September 6, 2017