ORLANDO--An assay that measures the proportion of free and bound
prostate-specific antigen (PSA) has been found to discriminate
between prostate cancer and benign conditions that elevate PSA,
thus reducing the rate of unnecessary biopsies, several research
groups reported at the American Urological Association annual
"It is about the best test that you can use to detect prostate
cancer in men with a mildly elevated PSA and a slightly enlarged
but benign-feeling prostate," said William J. Catalona, MD,
professor and chair of urology, Washington University School of
Medicine. "We've finally got a test that improves PSA specificity
without materially compromising its sensitivity."
At least eight presentations at the AUA meeting confirmed the
value of measuring the free-to-total PSA ratio, also known as
percent free PSA (PSAF).
The blood test measures the proportion of free vs complexed (or
bound) PSA. Untreated prostate cancer has been associated with
low percentages of the free form of PSA, while high percentages
of the free form most commonly occur with benign conditions. However,
there is a controversy over where the cut-off should fall.
Alan W. Partin, MD, associate professor of urology, Johns Hopkins
School of Medicine, found that using a PSAF cut-off between 16%
and 20% permitted detection of 90% of prostate cancers, while
reducing unnecessary biopsies by 30% to 40%.
But different PSAF cut-offs were proposed by some other investigators.
Dr. Catalona's series pointed to a cut-off value of 23%, which
insured that 90% of prostate cancers were detected, while 33%
of unnecessary biopsies were eliminated.
Joseph E. Oesterling, MD, professor and chair of urology, University
of Michigan, found that use of PSAF in a group of men with total
PSA levels between 3 and 4, who would not normally undergo biopsy,
increased prostate cancer detection by 44%. "Generally, the
cancers we found in this group were the early, curable cancers,"
Dr. Oesterling said. For patients with a total PSA level of 4
to 10 ng/mL, using PSAF reduced the number of negative biopsies
by 15%, he said.