Use of the PSA test is controversial. PSA is a protein produced by the prostate gland. High PSA levels in the blood can signal prostate cancer, but not always--sometimes a rise in PSA is due to another cause, and sometimes cancer can occur without a rise in PSA. About 20% of aggressive prostate tumors are found in men with normal PSA levels.

Further complicating the issue is the fact that in some older men, doctors advise a "wait and see" approach when prostate cancer is diagnosed. Because the cancer can be slow-growing, patients with limited life expectancies may not benefit from aggressive treatment.

Because PSA tests are not 100% reliable, the American Urological Association (AUA) recommends annual digital rectal exams in men aged 50 and older to screen for prostate cancer in addition to PSA testing.

At the meeting, researchers presented the results of a study conducted in Austria that showed that free annual PSA screening led to a 42% decrease in prostate cancer deaths there in 1998.

The screening program, begun in 1993, offered PSA tests to all men aged 45 to 75 in Tyrol, a region in western Austria. Two thirds of the 65,000 men eligible for participation were screened at least once during the first 4 years of the study.

Researchers at the University of Innsbruck, Austria, found that the incidence of prostate cancer in Tyrol peaked in 1994 and then declined. Since PSA screening began, more early stage cancers are being found and the number of potentially curable cancers has increased.

The number of 40- to 79-year-old men in Tyrol who died of prostate cancer remained constant from 1970 to 1993. Prostate cancer deaths decreased by 32% in Tyrol in 1997 and by 42% in 1998. Prostate cancer deaths for the rest of Austria remained the same as in previous years.

Dr. Georg Bartsch, principal investigator of the study, said PSA testing alone is a good way to reduce prostate cancer deaths. "Mortality dropped so much within 3 to 5 years because more early cases were found and therapy was offered to every one of those patients," he said.

In a second study presented at the meeting, researchers at the Washington University School of Medicine in St. Louis, Missouri, urged physicians to follow existing AUA guidelines on prostate cancer screening. AUA guidelines published in February recommend annual digital rectal exams and PSA tests in men aged 50 and older with no pre-existing prostate cancer. For men at higher risk, such as those with a family history of the cancer and African Americans, earlier screening is suggested.

The study enrolled 12,453 men aged 50 to 60 years who were screened between 1991 and 2000. This screening led to 1,571 of these men having a biopsy of their prostate, where tissue is removed for examination under the microscope. Testing showed that 165 of the men had prostate cancer, with 85% of the cases considered "potentially harmful."

"Using the guidelines, we're detecting important tumors in a localized and curable stage," said Dr. Robert L. Grubb, the study's principal investigator and a urology resident at Washington University School of Medicine.

A third report scheduled to be presented at the meeting on Tuesday also supports screening as a way of reducing prostate cancer deaths. A study from the National Cancer Institute showed that among American men, mortality rates from the cancer dropped by 16% among whites and by 11% among blacks during the 1990s.

"As is the case with most cancers, early treatment produces excellent results in patients with prostate cancer," said Dr. William J. Catalona, professor of urologic surgery at Washington University of School of Medicine and leader of the research team. "The 5-year survival rates of men treated for early prostate cancer are nearly 100%," he added in a statement.