This week the United States Preventive Services Task Force (USPSTF; what an acronym!) caused an uproar with their announcement of a “D” grade recommendation for the prostate specific antigen (PSA) blood test that is used to screen for prostate cancer. The group’s previous report was in 2008, in which the USPSTF recommended that men 75+ not undergo routine PSA screening. This recommendation caused little stir, because most prostate cancer experts agree that:
1. MOST (not all) prostate cancers are slow growing, usually taking well over a decade to spread and kill a man. Therefore, a man diagnosed in his mid-70′s with low-risk prostate cancer has minimal chance of dying of the disease, since the competing medical risks (heart disease, etc) are much higher.
2. There is no evidence in the medical literature that the PSA test saves the lives of these older men who undergo screening, then biopsy and treatment.
3. Prostate biopsies are uncomfortable and can cause infection which may rarely (<1%) be life-threatening.
4. The most common forms of treatment for prostate cancer, namely surgery and radiation therapy, have the potential to harm men. These harms include incontinence (leakage of urine), erectile dysfunction, and bowel irritation or damage. These are the basic downsides to PSA screening, subsequent prostate biopsies, and treatment.
The new October 2011 USPSTF recommendations are based on a review of the existing medical literature about PSA screening by an expert panel. The panel’s” review of the evidence” can be found at: http://www.uspreventiveservicestaskforce.org/uspstf12/prostate/prostateart.htm. The experts tried to address whether PSA-based screening decreases deaths due to prostate cancer (the ultimate question for any cancer screening test is whether lives are actually saved), as well as the potential harms and benefits of both PSA screening and prostate cancer treatment that follows screening. The new report is much more controversial than the 2008 report because the USPSTF extends their D grade for PSA testing across the board for all men. Prominent and powerful figures are weighing in on both sides of the debate: http://www.nytimes.com/2011/10/09/magazine/can-cancer-ever-be-ignored.html.
While the USPSTF analyzed a number of medical studies in order to generate their report, the major trials include the European ERSPC and American PLCO studies. I’ve discussed both of these studies in detail in When Cancer hits Home as well as Empowered Against Prostate Cancer: Treatment Guide with Patient Stories (http://thecancermd.com/store/). The European trial showed a 20% relative decrease in deaths due to prostate cancer thanks to PSA-based screening, while the U.S. trial failed to show a benefit. When scientists face this situation of conflicting results in medical studies, they usually turn to what’s called a meta-analysis, a type of study that groups multiple trials together in order to find an answer to the central question being asked. Thus far, the data are underwhelming for the life-saving potential of the PSA test in this statistical regard.
While there are several shortcomings of the PSA test itself, PATIENT SELECTION for PSA screening is the most critical factor for its success or failure. As location is to real estate, so patient selection is to cancer screening tests. Indiscriminate screening of all men over age 40 with the PSA blood test is now and always has been wrong. It subjects thousands of men to both psychological and physical harms that are unwarranted. Physicians need to use good judgment in determining which men might benefit from screening. Limiting those discussions to younger, healthier men will enhance the likelihood that if an abnormal PSA test results in a prostate cancer diagnosis, that subsequent treatment will prevent death due to prostate cancer. How much that group needs to be narrowed remains to be seen, but the validity of the process has been borne out for other cancer screening tests. The prime example that comes to mind is CT scan screening for people who are at high risk for lung cancer: http://www.cancer.gov/newscenter/pressreleases/2010/NLSTresultsRelease. In this major study limited to long-term smokers and former smokers, CT scan screening decreased the risk of dying from lung cancer by 20% relative to screening with chest x-rays.
In the long run, however, this current controversy about the PSA test for prostate cancer screening may soon be much ado about nothing. Recent improvements in diagnostic testing have been dramatic. In regard to prostate cancer specifically, I don’t think we’re a long way off from widespread availability of a test that will be much more accurate than the existing PSA blood test in predicting the presence and, just as importantly, the biologic aggressiveness of prostate cancer. Being able to sort out the majority of slow-growing prostate cancers from the minority that are literally man-eating will be a major medical success and one that can’t come a moment too soon.
- Patrick Maguire MD