2 Studies Conflict Over Value of Prostate Cancer Screening
WEDNESDAY March 18, 2009 -- Two new studies offer conflicting views on the value of screening men with a prostate-specific antigen (PSA) test to check for prostate cancer.
But at least one leading oncologist says this much seems to be clear: A younger man with a strong family history of prostate cancer should pay attention to a PSA test, while an older man with known medical problems can probably avoid the exam.
That assessment comes from Dr. Gerald Andriole, chief urologic surgeon at the Washington University Siteman Cancer Center in St. Louis, and lead author of one of the two papers on major PSA screening trials being released Wednesday by the New England Journal of Medicine.
But the reports are far from the final word on the issue of PSA screening, because there's a significant debate on the subject among the experts who know the most about it. Uncertainty is the prevailing mood, as demonstrated by the journal's decision to avoid the customary authoritative "commentary" on the study results, and instead run the transcript of a debate on the issue with two authorities, replete with "ifs" and "buts."
Start with the study results. The American trial, funded by the U.S. National Cancer Institute, followed almost 77,000 men. Half were recommended to have annual PSA tests for six years and digital rectal exams for four years, while the other half was told to have their usual medical care.
While 22 percent more prostate cancers were diagnosed in seven years in the PSA group, there were actually more deaths from prostate cancer in that group than in the usual-care group -- 50 to 44. And there were more deaths overall in the PSA group -- some of them possibly attributable to overtreatment of the prostate cancers, Andriole said.
The European trial, which included 182,000 men, offered either a PSA test every four years or no screening test at all. Over nine years, prostate cancer was diagnosed in 8.2 percent of the PSA group, and 4.8 percent of the no-screening group. The prostate cancer death rate was 20 percent lower in the PSA group.
The two studies can't be compared directly, Andriole said, largely because of differences in their designs. And neither answers the question: Is PSA screening worthwhile?
Dr. Christine Berg, a National Cancer Institute leader of the U.S. trial, said the problem is that while the PSA test can help diagnose prostate cancer, it can't single out the aggressive tumors that will eventually be fatal. The standard statement among doctors is that more men die with their prostate cancer than of it, and no current test can tell a slow-growing, not-dangerous tumor from an aggressive killer.
One recent study found that as many as two of every five men diagnosed with prostate cancer by a PSA screening test had tumors that were too slow-growing to ever be a threat.
"There is no test right now that can be done on blood or urine that will determine how aggressive a tumor is," said Dr. Edward P. Gelmann, professor of oncology at Columbia University Medical Center in New York City. "We're pretty good at identifying very aggressive tumors or very indolent tumors, but there is a large grey area."
"That kind of advance might be just around the corner," Berg said. "I do think we are making strides toward understanding the genetics of prostate cancer. The pace and rapidity with which we will get those answers is improving."
Meanwhile, men who have surgery or other treatments for nonaggressive prostate cancers face such problems as impotence and incontinence.
The death rate from prostate cancer in the United States has been dropping steadily since the early 1990s, when the PSA screening test was first introduced, Gelmann said, but there have been major improvements in treatment since then, so the effect of the PSA test is unclear.
The picture might become clearer as follow-up of the men in the U.S. study continues, Andriole said, because of the relatively limited follow-up time so far. "We just don't know what is going to happen to the youngest cohort of men in the study," he said. "We may see a benefit."
The message is clearest for older men, Andriole said. "If the man sitting in front of me is an elderly man with a limited life span, I can in good conscience tell that man that a PSA test is not necessary," he said.
There is a more complex message for younger men and their physicians, Andriole said. "I'm not confident we can tell younger men what to do," he said. "If they do have a digital rectal exam and a PSA test, then the physician's reaction needs to be less knee-jerk than it has been in the medical community so far -- to have a biopsy and the move directly to treatment if it is positive."
A PSA test measures levels of a protein produced by the prostate and thus is now cancer-specific, Andriole noted, and so, "if the results of this trial hold up, we may say that the PSA test is not a good indicator of prostate cancer."
Learn more about prostate cancer from the U.S. National Cancer Institute.
Posted: March 2009