Measuring mRNA in the abnormal gene enables better prediction of repeat prostate biopsy.

ORLANDO—A urine assay for prostate cancer gene 3 (PCA3) is superior to serum PSA tests for predicting outcomes of repeat prostate biopsy, data show.

Investigators studied 226 men with serum PSA levels of 2.5 ng/mL or higher and who had at least one negative biopsy. They collected urine specimens following digital rectal examination (DRE). The investigators measured PCA3 mRNA in the prostate cells released into the urine as a result of DRE.

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Repeat biopsy revealed prostate cancer in 60 men (27%). Using a PCA3 score cutoff of 35, the sensitivity and specificity of the PCA3 assay was 58% and 72%, respectively. A score of 35 and above was associated with a 3.6 times greater likelihood of a positive biopsy. At scores above 100, the risk of a positive biopsy was 50%.

The PCA3 score is a measure of the gene quantity corrected for the total genetic material from prostate cell nuclear material in the specimen. It is calculated by dividing the value for PCA3 mRNA by the value for PSA mRNA.

PCA3 score had no relationship to PSA levels or to prostate volume. “Apparently, the factors driving PCA3 levels are the not the same as those driving serum levels of PSA,” said lead investigator Leonard S. Marks, MD, of the Urological Sciences Re-search Foundation in Culver City, Calif. “Moreover, the performance of the PCA3 test does not seem to be dependent on the PSA range.” He reported findings here at the third annual Prostate Cancer Symposium.

In the future, he told colleagues, the PCA3 assay could be used to detect the development of prostate cancer in men with chronically elevated PSA but a negative prostate biopsy, which he referred to as a dilemma group.

A joint team from the University of Nijmegen in The Netherlands and Johns Hopkins University in Baltimore initially discovered and characterized the PCA3. Approximately 90% of all prostate cancers studied have so far tested positive for PCA3, the expression of which in prostate tumors is 60-100 times greater than that in adjacent benign tissue.

Gen-Probe, Inc., has developed a PCA3 mRNA urine assay that be-came commercially available in Europe in 2006.