New prostate cancer assay aids critical diagnostic decisions

July 1, 2006

Atlanta-A new prostate cancer test known as the PCA3 assay (Gen-Probe Inc., San Diego) remains a work in progress, but at this stage of development, it appears to offer significant utility in men with subtly elevated serum PSA (ie, ?2.5 ng/mL) but a negative initial biopsy.

The question these men raise is whether to watch and wait or to proceed to a second biopsy. Urologists now have a third option: the PCA3 assay.

Dr. Schalken and his team are credited with being the first to publish a description of the PCA3 gene in 1999. The assay that evolved from their discovery measures the mRNA of the prostate cancer-associated gene in urine expressed following a digital rectal exam.

Dr. Fradet explained that the assay works by quantifying PCA3 mRNA in voided urine and normalizing PCA3 levels to the amount of prostate RNA in the same sample using a prostate-specific "housekeeping" gene. The resulting ratio is then reduced by a multiplier (10-3 ) to yield the PCA3 score. The PCA3 score is correlated with prostate biopsy results, and different cutoff points yield varied specificities and sensitivities. Dr. Fradet's team calculated that a PCA3 score of 35 x 10-3 represented the optimal balance of specificity and sensitivity. In other words, a cutoff of 35 produced the greatest diagnostic accuracy.

Specific to prostate tissue

Whereas the study presented by Dr. Fradet showed the PCA3 test to have immediate applications, the other studies presented suggest a broader role for the assay in the future.