FDA Panel Recommends Approval Of New Version Of PSA Test To Detect Prostate Cancer

February 02, 1998

Washington, D.C., Feb. 2, 1998 -- An advisory panel to the Food and Drug Administration has unanimously recommended approval of a new test for detecting prostate cancer. Researchers say the "free PSA test" -- an updated version of the standard PSA test -- catches almost all prostate cancers and will be used as an aid to differentiate between prostate cancer and other benign prostate conditions.

"This test will help physicians find the cancer in its early stages, and patients who don't have cancer will be less likely to undergo biopsies," says William Catalona, M.D., professor of surgery and head of the Division of Urologic Surgery at Washington University School of Medicine in St. Louis. Catalona, the first to establish the standard PSA test as a screening tool, was the lead researcher in a recent multi-center trial of the free PSA test. The latter measures the amount of PSA (prostate specific antigen) that floats freely in the blood.

According to the study, the free PSA test detects 95 percent of prostate cancers, and the cancers it misses are likely to be small and not life threatening. The study also showed that the free PSA test could reduce the number of unnecessary biopsies by 20 percent. Catalona presented the study results to an FDA panel today. The recommendation for approval came just five months after the data were submitted for review. The average FDA review time for medical devices has been 26 months until recently, as the FDA has made efforts to decrease review times.

The study, conducted at seven medical centers across the country, involved 773 men between the ages of 50 and 75 who had undergone biopsies to determine whether prostate cancer was present. Before the biopsy, physicians drew blood samples from each patient and made two different measurements of PSA, a protein that can be mass-produced by a cancerous prostate.

In addition to the standard PSA test, which involves measuring the total amount of PSA in the blood, they measured "free PSA," the percentage of PSA that is not bound to other proteins. Previous studies had shown that PSA produced by cancerous prostates is particularly likely to cling to other proteins. Therefore, a low percentage of free PSA could be a sign of cancer.

Only men who had standard PSA levels between 4 and 10 and unsuspicious digital rectal exams were included in the study. Treatment of such patients has been controversial since they have an intermediate level of risk. These patients generally receive biopsies, but only 30 percent will actually have cancer. Many of the others will have benign prostatic hyperplasia, a common swelling of the prostate that also can make PSA levels rise. "The biggest criticism of the PSA test has been that it isn't specific enough," Catalona says. "Too many suspicious readings have nothing to do with cancer, which means too many cancer-free men undergo painful and expensive biopsies."

Researchers discovered that almost all of the patients with cancer had free PSA levels that made up less than 25 percent of the total PSA detected. If physicians had biopsied only these patients, they would have caught 95 percent of the tumors and cut down the number of negative biopsies by 20 percent. The small group of patients who had cancer but exceeded the 25 percent cutoff were generally older and had low-grade tumors. "For these patients, the best course of action is often watchful waiting," Catalona says. "The free PSA test helps identify the patients who could really benefit from surgery or other treatments."

Catalona believes physicians should still use the standard PSA test for initial prostate cancer screenings. The patients in the gray area of 4 to 10 should then take the free PSA test instead of automatically undergoing a biopsy, he says.

A prostate biopsy costs about $1,200, so wide use of the new test could lead to huge savings, Catalona says. It is not known how much the free PSA test, officially called the Tandem Free PSA test, will cost. Like the standard PSA test, the latest version was developed by Hybritech Inc., a San Diego-based subsidiary of Beckman Coulter in Fullerton, California. Hybritech Inc. funded the free PSA test research.

Washington University School of Medicine runs the largest prostate cancer screening study at a single institution in the nation. More than 32,000 men have been enrolled. The other centers that participated in the clinical trial of free PSA are Baylor College of Medicine in Houston, Harvard University in Boston, Johns Hopkins University in Baltimore, Loyola University in Chicago, University of California - Los Angeles, and the University of Washington in Seattle.

Prostate cancer is the most commonly diagnosed cancer in American men and the second deadliest. In 1998, an estimated 184,500 American men will learn they have prostate cancer and more than 39,200 American men likely will die from the disease.
-end-


Washington University School of Medicine

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