Doesn't distinguish aggressive tumors from slow-moving malignancies
MONDAY, May 3 (HealthDay News) -- A technique that urologists had hoped would make it possible to distinguish men with prostate cancer who need treatment from those who would only need watchful waiting didn't work well, researchers report.
The technique, called PSA kinetics, measures changes in the rate at which the prostate gland produces a protein called prostate-specific antigen. A significant increase in PSA kinetics, measured by the time during which PSA production doubles or increases at a rapid rate, is supposed to indicate the need for treatment, by radiation therapy or surgery.
PSA kinetics has long been used to measure the effectiveness of treatment. A number of cancer centers have started to use it as a possible method of distinguishing aggressive cancers that require treatment from those that are so slow-growing that they can safely be left alone.
Recent studies indicating that many men with slow-growing prostate cancers undergo unnecessary treatment have given urgency to the search for such a tool, especially considering that side effects of treatment can include incontinence and impotence.
But the study indicates that "PSA kinetics doesn't seem to be enough to show you who you should follow and who you should treat," said Dr. Ashley E. Ross, a urology resident at the Johns Hopkins University Brady Urological Institute, and lead author of a report on the technique published online May 3 in the Journal of Clinical Oncology.
The report describes the results of PSA kinetics measurements of 290 men with low-grade prostate cancer -- the kind that often doesn't require treatment -- for an average of 2.9 years. The results of PSA tests were compared with biopsies -- tissue samples -- that measured the progression of the cancers.
The trial is part of a study, under supervision of Dr. H. Ballentine Carter, director of the division of adult urology at the Brady Urological Institute, that began in 1994. Men in the trial had PSA tests every six months and biopsies every year.
"PSA values do not predict progression by biopsy," Ross said. "There were huge overlaps between people who had higher or lower values. They were not predictive of if you had more disease or more aggressive disease."
And so the findings do not support the hope that PSA kinetics might lessen the need for frequent biopsies, Ross said. "You need to biopsy these men yearly or less than that," he said.
But the issue is still open, said Dr. Jared Whitson, a clinical instructor in urology at the University of California, San Francisco, who wrote an accompanying editorial.
There might have been "selection bias" in the study, Whitson said, since many men under watchful waiting at the institute were not included in the trial. "We don't know a lot about the 300 patients who were in active surveillance but not included in the trial," he said.
In addition, "there is some prior evidence to suggest that PSA kinetics are associated with biopsy progression," Whitson said.
There was such evidence in a Canadian trial, Ross acknowledged, but "in the Canadian study there were men with a lot more cancer than we would be comfortable following. We only select men with very little cancer."
So it is too early to give up on PSA kinetics as a method of determining who should be treated, Whitson said. But it is only one of the tools that should be used to make a decision, he said. "There is no one feature or factor which can singlehandedly prompt intervention," Whitson said. Other standard markers, such as Gleason score, a measure of a cancer's degree of disorganization, must also be used, he said.
For a complete rundown on prostate cancer, visit the U.S. National Cancer Institute.
SOURCES: Ashley E. Ross, M.D., Ph.D., urology resident, Johns Hopkins University, James Buchanan Brady Urological Institute, Baltimore; Jared Whitson, M.D., clinical instructor, urology, University of California, San Francisco; May 3, 2010, Journal of Clinical Oncology, online
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