[-2]Proenzyme Prostate Specific Antigen Is More Accurate Than Total And Free Prostate Specific Antigen In Differentiating

Main Category: Prostate / Prostate Cancer
Also Included In: Urology / Nephrology
Article Date: 24 Jul 2010 - 15:00 PDT

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UroToday.com - Prostate Specific Antigen (PSA), the primary means of diagnosing prostate cancer in the modern era, lacks specificity in differentiating benign from malignant disease. Thus clinical decisions based on PSA may lead to unnecessary biopsies in some while overlooking biopsies in others. p2PSA has emerged from studies looking at archived serum samples over the past several years as a better screening tool for detecting prostate cancer.

Our study sought to validate the potential of p2PSA in a prospective screening study among a contemporary cohort of men. The advantages of this approach are that it minimizes sampling and storage bias, while allowing side-by-side comparison against PSA and free PSA in a prospectively screened population. Additionally, calculations as to the positive and negative predictive value can be made based on the incidence of prostate cancer. We demonstrated that p2PSA (AUC = 0.76) was superior to PSA (AUC = 0.50) and free PSA (AUC = 0.68). p2PSA had a positive predictive value of 54.8% and had a negative predictive value of 85.7% outperforming PSA (PPV 45.1% and NPV 75%).

However, there are some important limitations to its clinical use that should be noted, especially as p2PSA is underway with FDA trials and may enter clinical practice. All clinical studies to date on p2PSA have used this serum assay in conjunction with conventional total PSA. Thus, despite p2PSA's superior screening characteristics in terms of sensitivity and specificity, there is no evidence to date to supplant PSA as the primary screening tool for prostate cancer. Additionally, clinical cutoffs still need to be determined in larger populations before interpretation of individual p2PSA values can be made.

A specific niche that our research group feels p2PSA could fill would be of patients with a total PSA of 2 to 4, a group of particular diagnostic uncertainty. p2PSA's negative predictive-value could be used to determine the need for biopsy with a low p2PSA suggesting a low-likelihood of CaP being discovered on biopsy. At the same time, this same group with elevated p2PSA values is more likely to have CaP as well as increased likelihood of aggressive cancers as described by Catalona et al. (J. Urol 2004).

At time of publication, several independent research groups have obtained similar results with p2PSA demonstrating superior sensitivity and specificity to currently available assays. P2PSA recently gained approval for use in Europe, and we anticipate similar approval in the United States pending FDA trials. This study adds important information to support its clinical use because it uses p2PSA as it would be used clinically, as a screening tool, and validates previous results.

Written by Brian Le, MD and William J. Catalona, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations, etc., of their research by referencing the published abstract.

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