printable versionIs PSA test a lifesaver or of little use?
BY MITZI BAKER
Urology professors Joseph Presti and Thomas Stamey disagree about the value of the PSA test.
Virtually every man will get prostate cancer if he lives long enough. This sobering fact has both an obvious bad side and a not-so-bad side that underscored conflicting presentations by two professors of urology at the Department of Medicine's grand rounds meeting in Fairchild Auditorium Thursday.
Joseph Presti, MD, gave greater weight to the bad side—that prostate cancer can be deadly, with 32,000 men dying of it in the United States each year. But Thomas Stamey, MD, focused on the not-so-bad side—of the 232,000 cases diagnosed each year, the majority of the men have a slow-growing form of the disease that would not be likely to ever escape from the prostate or cause any noticeable problem.
What has led these different assessments of the potential risks to become what some in the field call "the great prostate debate" is how physicians should decide which of the thousands of cases warrant treatment and which warrant nothing beyond watchful waiting. At the heart of the matter is a widely used diagnostic test for a prostate-specific antigen that indicates the presence of cancer, known as the PSA test, which has lately been called into question.
Stamey, whose presentation led off the event, is an unlikely critic. In 1987 Stamey published the first paper claiming that PSA levels could be used as an indicator of prostate cancer, but his research over the years has led him to contend that the test is all but useless in predicting cancer severity.
Stamey has come to believe that elevated PSA levels (between 2 and 10 ng/ml) actually reflect a condition called benign prostatic hyperplasia, a harmless increase in prostate size. He published his conclusions in the Journal of Urology in 2002 and 2004.
In his talk, Stamey explained that the basic dilemma is that men who have elevated PSA levels frequently undergo biopsy, which will almost always find cancer.
"If we all have it, all you need is an excuse to biopsy the prostate and you're going to find it," he said. "You want to be careful about being biopsied because the odds are against you" being found free of cancer.
Finding cancer does not necessarily indicate that prostate removal or radiation treatment is required, Stamey emphasized.
The main reason why the detection of cancers that might never cause a problem is a problem in itself is that the treatment is not without side effects. The gold standard for treatment is complete removal of the prostate—radical prostatectomy—which is tricky surgery and can leave a man impotent and/or incontinent.
But Presti, who presented following Stamey, has a more favorable view of the test. "There is no question in my mind that the PSA test is not a perfect test," he said. "But is it such a bad test?"
Presti then answered his own question: "In my mind, the PSA test has made an impact on prostate cancer mortality. We know that early detection translates to improved survival."
Presti, associate chair of the Department of Urology and director of the Division of Urologic Oncology, presented data showing that the rise in the use of the PSA test to screen men corresponds to a decrease in the death rate. He also pointed out that cancers detected by screening tend to be caught earlier and can be more curable.
Still, Presti acknowledged that such statistics are not the final word. Those numbers don't take into account whether many of the men who received treatment would have lived without it. He said that the effect of screening on prostate cancer mortality could only be established in prospective randomized clinical trials, in which a large number of men are tracked over many years to see who develops prostate cancer. Two such trials have been initiated—one in Europe and one in the United States. Results of those trials will not be available for several years.
Although neither doctor discussed treatment options in detail, Stanford researchers are continuing to improve on techniques to treat prostate cancer, including using such new forms of radiation therapy as the CyberKnife, a radiosurgical machine that uses high-voltage electrons to kill tumors. Presti and his colleagues treat hundreds of prostate cancer patients each year, and they specialize in nerve-sparing radical prostatectomy, which lessens the likelihood of impotence and incontinence.
And regardless of their differences, both men agreed that what makes the decision about how to use the PSA results so difficult is that there isn't anything today better than the PSA test for detecting prostate cancer. While doctors can use a digital rectal exam to locate the largest tumors, those arising on the far side of the prostate may be hard to detect.
One hopeful development came last year in an article in the New England Journal of Medicine in which a team led by a researcher at Harvard School of Medicine found one way that PSA numbers could be particularly useful. They suggested that by following the rate of change of a man's PSA number, doctors could track the progression of prostate cancer.
Still, the two urologists said that a better marker is needed. What would be ideal would be to find an easily detectable indicator that would not only unequivocally tell if cancer is present, but also how aggressive it is. Several researchers at Stanford, including Stamey, are taking advantage of the latest in DNA microarray technology to identify which genes are turned on and off in prostate cancer.
