US advice on PSA screening

Forty years after prostate-specific antigen (PSA) was identified and nearly 20 years after it became available for prostate cancer screening, the US Preventive Services Task Force (USPSTF) recently recommended against PSA-based screening.¹ In the interim, millions of men have been tested. Because PSA is not cancer-specific and because prostate cancer’s aggressiveness varies widely, controversy and debate about PSA screening were predictable from the outset.

The American Cancer Society advises clinicians to provide “information about the uncertainties, risks, and potential benefits” to help men “reach a screening decision based on their personal values”. But the idea that physicians could initiate truly informed discussion was wishful thinking, because clinicians and patients had to consider an enormous list of probability estimates and uncertainties: What PSA cut-off is best? What level should trigger repeat PSA testing or biopsy? How often should we repeat either? What is the patient’s pretest probability of cancer? What is the chance that a PSA test plus a biopsy will find cancer, if it exists? Will any cancer found be clinically important? Will this patient prefer surgery, radiation therapy or watchful waiting? What are the probabilities of serious side-effects from each treatment, and how will this patient weigh them? Most importantly, will screening reduce this patient’s risk of death from prostate cancer?

Thus, patients were not really making informed decisions, and office-based discussion of the pros and cons of PSA testing was essentially a charade. Instead, most patients’ decisions reflected their general concerns about cancer or their general inclination to accept (or resist) medical interventions.

In March 2009, initial results of the two major screening trials were finally available. Unfortunately, they created more confusion than clarity. A US trial showed no mortality benefit from screening; a European trial showed a small reduction in prostate cancer-related mortality, but large numbers of men received aggressive treatment to benefit few. Both trials had important methodological limitations (addressed by the USPSTF). Discussions with patients about screening have therefore become even more difficult, since clinicians must now add another layer of uncertainty: explaining why two huge randomised trials were less than definitive and why experts disagree about their interpretation.

A second issue lies at the interface of clinical practice, public health and responsible stewardship of healthcare resources. Although the USPSTF explicitly does not consider costs, policymakers cannot ignore economic aspects of screening. Using data from the European screening trial, researchers have estimated that €3.86 million ($5.2 million) would have to be spent on screening (and the interventions that follow it) to prevent one death from prostate cancer. 

That estimate does not appear to include the costs of excessive serial PSA testing and repeated office-based encounters to discuss screening or interpret fluctuating PSA results. The extraordinary time, effort and costs associated with the PSA-screening enterprise must be evaluated against other claims on healthcare spending and physicians’ time and energy. For two decades, primary care physicians have been expected to present a flawed screening test to patients, cloaking the flaws in an elaborate ritual of informed decision-making. In turn, men have been expected to make sense of a confusing mix of hypothetical outcomes. Although the USPSTF recommendation is unlikely to end the PSA controversy, a document finally exists that should provide guidance to clinicians and policymakers.

Reference

1. Screening for prostate cancer: draft recommendation statement. Rockville, MD: US Preventive Services Task Force 2011.