"Free" PSA Test May Reduce Need for Some Prostate Cancer Biopsies

May 20, 1998: A new test that measures the percentage of "free" PSA in a man's blood could spare up to 200,000 American men a year a surgical biopsy to detect cancer. The test was tried out on 773 men whose prostates felt normal on digital rectal exam, but whose standard PSA levels were elevated between 4 and 10.

     "These are the men in the diagnostic grey zone," said researcher Alan Partin, M.D., Associate Professor of Urology at Johns Hopkins. "They're at risk for prostate cancer on the basis of the PSA levels, but experience shows that 75 percent of the time, their biopsies will be negative for cancer."

Elevated PSA levels may indicate prostate cancer. But especially in the grey zone, high PSA can be caused by other factors like infection (prostatitis) or a common condition in older men, benign prostatic hyperplasia (BPH). If PSA elevated by a noncancerous condition can be identified, those men can be spared biopsy.

F-PSA Test Significantly Reduces False-Positive Rate of Standard PSA Test

The PSA test measures prostate-specific antigen, a protein produced only in the prostate gland. Quick and simple to undergo, a regular PSA test costs less than a mammogram. But the "false positives," requiring biopsy, add expense, uncertainty and a more invasive procedure.

The "free" PSA test measures PSA that is not bound to other proteins in the blood. This "free" PSA is present at significantly lower levels in men with prostate cancer than in men who have the benign condition. Used together, the study found, the newer "free" PSA and the traditional PSA screening can detect 95 percent of prostate cancers while eliminating many false positives and unnecessary biopsies.

The multicenter trials were led by William J. Catalona, M.D., of Washington University School of Medicine, St. Louis and paid for by Hybritech Inc. of San Diego, CA., a test manufacturer. The report appeared in the May 20, 1998 issue of the Journal of the American Medical Association.

Dr. Catalona is known worldwide for determining that the PSA test is the single most accurate method for detecting prostate cancer.  Screening with the PSA test, while still controversial, has become widespread since the early 1990s, and Catalona runs the largest prostate cancer screening program in the country.

"Now we can figure with more accuracy who not to biopsy," Dr. Alan Partin said. Partin said: "The study demonstrated that men in the diagnostic gray zone should probably be biopsied only if their percentage of FPSA is at or below 25 percent." "At that level," he said, "we can detect 95 percent of cancers while excusing men with benign diseases from the need for a biopsy."

     Prostate cancer screening tests must be sensitive enough to find as many potentially curable cancers as possible. "By using this test to zero-in on men in a certain group most likely to have active cancer," Partin said, "there is the potential to cut the cost of prostate screening dramatically. We also spare those men the possible complications of biopsies."

Partin is the creator of the Partin Tables, a tool used on the Internet by prostate cancer patients to make more informed treatment decisions with their doctors. A newly-diagnosed and staged patient can locate his PSA value on the Partin tables and find the intersection with his Gleason score and clinical stage. He can then read off Dr. Partin's estimate of the percentage probabilities of whether this cancer is organ-confined or has escaped the capsule.

Use of the Percentage of Free Prostate-Specific Antigen to Enhance Differentiation of Prostate Cancer From Benign Prostatic Disease: A Prospective Multicenter Clinical Trial W. J. Catalona, St Louis, Mo; A. W. Partin, Baltimore, Md; K. M. Slawin, Houston, Tex; M. K. Brawer, Seattle, Wash; R. C. Flanigan, Maywood, Ill; A. Patel, Los Angeles, Calif; J. P. Richie, Boston, Mass; J. B. deKernion, Los Angeles, Calif; P. C. Walsh, Baltimore, Md; P. T. Scardino, Houston, Tex; P. H. Lange, Seattle, Wash; E. N. P. Subong, Baltimore, Md; R. E. Parson, G. H. Gasior, K. G. Loveland, P. C. Southwick (Hybritech), San Diego, Calif

Hot Paper in The Scientist October 1997: William Catalona talks about his own paper on Free PSA to reduce unecessary biopsies [opens in new browser window].

The FDA approved Hybritech's "Free" PSA blood test largely on this study's results.

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