How should men interpret the conflicting news over the value of the PSA test? Is that prostate cancer screening test worthwhile?
Two clinical studies (one in the United States and one in Europe), both dealing with prostate-specific antigen screening, were recently published in the online version of the New England Journal of Medicine and have caused considerable discussion.
These represent the first reports from two large, randomized trials, which many doctors and patients alike had hoped would resolve important questions about the upside and downside of PSA screening in "healthy" men, i.e., men who are being screened for primary prevention. In the United States, a very substantial proportion of men over the age of 50 undergo such screening on a routine basis. Some physicians have critiqued the publication of these studies now, as opposed to allowing the studies to unfold for a longer time span, precisely because of the uncertainty and lack of closure likely to arise among patients, doctors, and health policy experts. It is possible that some of the issues can be resolved as more time elapses in both trials. That said, the studies have been published, and the public needs to absorb the results.
In the U.S. study, known as the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, the investigators reported no overall mortality benefit (that is, no reduction in rates of death due to prostate cancer) from a program of combined screening with PSA testing and a doctor's direct examination (digital rectal exam) during a follow-up of just over 10 years.
In the other, the European Randomized Study of Screening for Prostate Cancer (ERSPC) trial, PSA screening (this time without digital rectal exam) achieved a 20 percent reduction in mortality from prostate cancer at a follow-up of just under 10 years. This amounted to an absolute reduction of about 7 prostate cancer deaths per 10,000 men screened. The designs of the two trials were a little different, but it is not known precisely how such differences might explain the results.
In the American study (the one with no significant effect on prostate-cancer-related death rate so far), the relatively low number of prostate cancer cases may lead to a form of statistical uncertainty about a modest benefit that was missed.
Other significant possible explanations for the results may be a high level of "prescreening" in the patient population and a certain amount of PSA testing done in the control group, which wasn't supposed to undergo screening. In a democracy, it is an impossibility to mandate or obtain a "pure" control group for such studies, and for that, we should be grateful. Still, life is sometimes complicated by this reality. Roughly half the men in the "control" group were apparently undergoing PSA testing by year five, perhaps either self-motivated or on their private doctors' recommendations. Still other possible considerations are that improvements in modern therapy could, at least partially, ameliorate the death rate once a new case of prostate cancer is diagnosed, even if no routine PSA screening had been involved in the bargain.
Moreover, heart disease and related disorders constitute "competing" causes of death in men at risk for prostate cancer, who might be more likely to die with prostate cancer than from it.
So, after taking a look at these results, where does that leave the patients and their doctors?
Many authorities believe that routine PSA screening causes at most a modest effect on death due to prostate cancer. That is not to say, however, that a physician's offer of routine PSA screening should be disparaged. There is room for disagreement among doctors of goodwill on how to interpret and act on the results published so far. There is, nonetheless, a downside in potential overdiagnosis and overtreatment, which are nontrivial issues. In the European study, over 1,400 men would need to undergo the PSA screening test, and then around 50, give or take, would need to undergo therapy, in order to prevent one death due to prostate cancer per se during the ensuing 10 years. Patients and their doctors will need to discuss these observations and individualize decision making on PSA screening accordingly.
In medicine, there are times when highly qualified doctors—equally knowledgeable and committed to the welfare of the patients in their care—look at the same data and reach different conclusions. This is one of those times.
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