FDA has cleared for marketing a molecular test that may help reduce the need for repeat biopsies and their associated complications for men with previous negative prostate biopsies. The new prostate cancer gene 3 (PCA3) assay is the first urine-based molecular diagnostic assay approved as a decision aid for possible prostate cancer. PCA3 is a protein produced only in the prostate gland, a walnut-shaped structure in men that is below the bladder. This test, which has been available in Europe for several years, measures the urine level of PCA3 messenger RNA (m-RNA), a signal from genes that tells the prostate to produce the PCA3 protein. Increased amounts of the m-RNA (over-expressed) are produced by 95% of prostate cancer cells.
The PCA3 test does not provide a definitive answer as to whether a man has a cancer or not. A positive biopsy remains the gold standard in diagnosing prostate cancer. Rather, the test is intended for use in men 50 years of age or older who have high prostate-specific antigen (PSA) values and one or more previous negative prostate biopsies for whom repeat biopsies would usually be recommended. Prostate biopsies can sometimes have false-negative results, leading to the need for repeat procedures.
The recently approved test compares the amount of PCA3 messenger RNA (m-RNA) to the the level of PSA RNA in the first urine sample collected after a digital-rectal examination (DRE). Labs report a score based on the ratio of PCA3 RNA to PSA RNA called the PCA3 score. Doctors consider the test results in conjunction with other laboratory and clinical data to determine the likelihood that a repeat biopsy will be positive.
In a multicenter study of the test's performance, 49.6% of 466 subjects had PCA3 scores less than 25. Of these men, 90% subsequently had a negative biopsy result, while 10% had a biopsy positive for prostate cancer. Of the 235 men with PCA3 scores over 25, 34% had positive biopsies and 66% had negative biopsies. The results suggest that scores less than 25 indicate decreased likelihood of a positive repeat biopsy result, so patients with such scores might consider delaying repeat biopsies.
The PCA3 test may help doctors and their patients with elevated PSA levels make decisions about care related to possible prostate cancer. These choices are often difficult and confusing. Although PSA can help detect cancer, there are sometimes false-positive results, and major health organizations disagree on the usefulness of PSA for prostate cancer screening. Biopsies used in follow-up to positive PSA results to diagnose cancer can cause discomfort, anxiety, and sometimes complications. Their accuracy depends on the number of tissue samples and the sites from which they are taken. Concerns over missing clinically significant cancer may prompt additional biopsies. As the PCA3 test gains wider acceptance, it may aid some men and their doctors in decisions about their future care.
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Prostate Cancer Overview. American Cancer Society. PDF available for download at http://www.cancer.org/acs/groups/cid/documents/webcontent/003072-pdf.pdf. through http://www.cancer.org. Last revised June 20, 2011. Accessed March 6, 2012.
Groskopf J, Aubin SM, Deras IL et al. APTIMA PCA3 molecular urine test: development of a method to aid in the diagnosis of prostate cancer. Clin Chem 2006;52: 1089-95.
Physician Brochure for the PRoGensa® PCa3 assay. Gen-Probe. PDF available for download at http://www.gen-probe.com/pdfs/pi/L692-MKT.pdf through http://www.gen-probe.com. Accessed March 8, 2012.
News article. Federal Task Force Advises Against Use of PSA Test for Screening. Lab Tests Online. Published October 11, 2011. Accessed March 8, 2012.