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PCA3 Molecular Urine Assay for Prostate
Cancer in Men Undergoing Repeat Biopsy
(May 2007)
In this article a
consortium of researchers, including Dr. Bill Ellis, University of
Washington, report the evaluation of the performance of newest iteration
of this assay. The earlier version, UPM3, was reviewed in the April 2006
PCa Commentary: "UPM-3 A diagnostic urine test with greater accuracy for
cancer detection than PSA. The biologic basis of the test is the
identification in urine of an epitope on mRNA from the PCA3 gene, a gene
"highly overexpressed in PCa tissue compared with benign prostate
tissue." The PCA3 test quantitates the ratio of the number of copies of
PCA3 mRNA to those of mRNA for PSA, the latter taken as a representative
surrogate for the totality of benign and malignant prostate tissue. A
test result is presented along a continuum range of <5 to >100.
Statistical analysis suggested a score of 35 as the optimal cutoff,
which "provided high specificity (72%), preserved sensitivity (58%), and
yielded an odds ratio of 3.6." A PCA3 score of <5 was associated with an
~11% likelihood of a positive repeat biopsy; a score between 20-34,
~22%; and between 50 and 100, an ~45% likelihood.
The goal of the study
was to compare the efficiency of the PCA3 test against the standard PSA
(at a comparison cut-point of 4 ng/mL) in predicting the likelihood of
finding cancer on a repeat biopsy in men whose initial PSA values had
triggered a biopsy, but in whom at least one previous 12-core biopsy had
been negative. Urine specimens from 226 men whose PSA values were > 2.5
ng/mL were studied (median PSA: 6.1 ng/mL ; range 2.5 - 31.1). The
specimens were informative in 97% of the men. Cancer was found in 60
(27%) on repeat biopsy.
In a comparison based
on their respective "areas" plotted on the receiver operating curve
graph, the performance of the PCA3 test showed greater predictive
efficiency, 0.678, vs. 0.524 for PSA, the latter "indicating little
better than a 'coin toss' probability of predicting the presence of CaP."
As stated in the
article, "25% of CaP cases remain undiagnosed after a single set of core
biopsies." Improved predictability of detection could reduce the
morbidity and expense of the exercise of re-biopsy by permitting greater
selectivity
For further information
about obtaining the test material and processing contact the Bostwick
Lab representative, Ms. Bonnie Scott, at 206-853-2573
Bottom Line:
The authors conclude: "For men with elevated serum PSA levels who are
undergoing repeat prostate biopsy, the PCA3 assay appears to represent
an incremental improvement in the ability to predict the prostate biopsy
outcome."
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