News Release

New Version Of Blood Test Clarifies Prostate Cancer Risk

Peer-Reviewed Publication

Washington University School of Medicine

St. Louis, May 20, 1998 -- Most men can obtain a good estimate of their prostate cancer risk from the traditional blood-screening test. But about 9 percent have borderline results and may undergo unnecessary biopsies. A large, multicenter study led by a researcher at Washington University School of Medicine in St. Louis suggests that a new version of the screening test clarifies the prostate cancer risk of these men and provides a single cutoff value that can detect 95 percent of prostate cancers. The results were published today in the Journal of the American Medical Association.

Lead author William J. Catalona, M.D., professor of surgery and director of the Division of Urologic Surgery, was first to establish the standard PSA test as a screening tool. He says the findings in the clinical trial of 773 men should reduce needless biopsies by 20 percent. "By eliminating these biopsies, you're not only going to save money, but you're going to spare men the anxiety of a false alarm and the discomfort of going through an unnecessary procedure," Catalona says.

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.

Doctors have used the traditional screening test -- called the PSA test -- since the early 1990s to detect total blood levels of a protein called prostate-specific antigen (PSA). Levels of this protein can be elevated in prostate cancer. But doctors have been unable to confirm or rule out the disease without a biopsy for men whose total PSA levels fall between 4 and 10 ng/ml. Prostate biopsies, which cost about $1,200, have shown that up to 75 percent of these men do not have cancer.

The new PSA test, combined with results from the traditional test, can help distinguish between prostate cancer and other factors that raise PSA levels, such as a noncancerous condition called benign prostatic hyperplasia. It measures a free-floating form of PSA whose levels in blood are significantly lower in men with prostate cancer than in men with the benign condition.

The 773 study participants had scores on the traditional PSA test of between 4 and 10 ng/ml. Doctors conducted the new PSA test on these men to determine what proportion of their PSA was floating freely. The men then underwent biopsies. Ninety five percent of those found to have prostate cancer had 25 percent or less of their antigen as free PSA.

"The cancers you tend to miss with the 25 percent cutoff are the less aggressive ones in older men, and they can be caught with follow-up PSA tests," Catalona says.

The study also revealed that combining the two PSA tests provides insight into the severity of prostate cancer. The lower the percentage of free PSA, the more aggressive the cancer.

The study was funded by a research grant from Hybritech Inc., a subsidiary of Beckman Coulter of Fullerton, Calif. Hybritech manufactures the standard PSA test and the free PSA test, officially called the Hybritech Free PSA Test.

Although the 25 percent cutoff for free PSA works well, the significance of a particular score depends somewhat on a man's age, prostate size and total PSA level. The researchers therefore have provided prostate cancer risk assessments for different free PSA ranges that take these factors into account. "You can give patients individual risk assessments of the likelihood that a biopsy would reveal prostate cancer," Catalona says. "The tests provide patients with the power to make more informed decisions about their care."

Based on the study's findings, the U.S. Food and Drug Administration granted approval in March for use of the Hybritech Free PSA Test.

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 the free PSA test are: Baylor College of Medicine in Houston, University of Washington in Seattle, Loyola University in Chicago, The Johns Hopkins Hospital in Baltimore, University of California-Los Angeles and the Harvard Program in Urology at Brigham & Women's Hospital in Boston.

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