The debate about PSA screening for prostate cancer re-erupted in July 2016. That’s when a sketchy study by researchers from Northwestern University in Chicago showed that the “incidence” of metastatic prostate cancer rose significantly during the past decade and suggested this was due, at least in large part, to recommendations against PSA (prostate specific antigen) screening by the influential U.S. Preventive Services Task Force.
The study got widespread news coverage, which often echoed the university’s press release (alarmingly headlined “Metastatic Prostate Cancer Cases Skyrocket”) and its singling out of “lax screening” as a likely culprit for this delay in diagnosis until cancers had already spread. This was the smoking gun some PSA proponents were undoubtedly looking for—proving that the Task Force’s anti-screening guidance would lead to more advanced cancers and thus more deaths.
If you’re a man who stopped having routine PSA blood tests after the Task Force advised against it in 2012, you may have shuddered when you read this news. But the study did not prove anything. It looked at a cancer database of patients from 1,089 facilities nationwide and, yes, it found that cases of metastatic prostate cancer rose about 70 percent between 2004 and 2013 (low-risk cancers declined and intermediate- and high-risk cancers remained fairly stable). Yet these numbers mean little without knowing the size of the overall pool of men each year, which was not provided. “Incidence” is the rate of occurrence per a specific number of people (usually 10,000 or 100,000) over a period of time. There’s no “per” here.
There are many reasons why these raw numbers may be rising—a growing and aging population, improved ability to diagnose metastatic cancer early on, or even an increase in the aggressiveness of prostate cancers, for unknown reasons. Other databases have not found an increase in the incidence of metastatic prostate cancer at first diagnosis, though we don’t yet have published data for the past couple of years. And I’ve seen no indication that deaths from prostate cancer have been rising, after years of steady declines. That would be an unmistakable warning sign.
In any case, it makes no sense to blame the Task Force for the uptick in advanced prostate cancer proposed by this study. In its 2002 and 2008 guidelines, the Task Force said there was insufficient evidence to recommend for or against routine PSA screening. It wasn’t until mid-2012 that it recommended against screening, concluding that the risks of overdetection and overtreatment of harmless tumors outweighed the benefits, which were still unclear. That probably led to decreased screening—but years after the increase in advanced cancers reported in the new study. What’s more, any uptick will probably take at least five years to become apparent, and even longer for mortality rates to rise, if that happens.
PSA screening remains an open question. It still is not clear how many lives it saves. The Task Force has been attacked for its interpretation of the two major clinical trials upon which it largely based its guidance. It is now re-evaluating the research for its next set of guidelines, expected in 2018. At the same time, experts are trying to find ways to maximize the benefits of screening with PSA and other tools while minimizing its harms by, for instance, not treating “low-risk” cancers, and using a “watchful waiting” approach (also called active surveillance) more often.
Meanwhile, we agree with the American Cancer Society (ACS) that the choice of whether to be screened is up to each individual man, who should discuss the potential benefits, harms, and uncertainties with his doctor. Good places to start are these ACS decision guides, as well as our article about the Task Force’s recommendations.
We’ll keep you informed as the PSA picture becomes clearer.