Feb. 23 (HealthDay News) -- Physicians may soon be able to identify which men have a more deadly form of prostate cancer, U.S. researchers report.

More than one million prostate biopsies are performed each year, note a team from Oregon Health & Science University (OHSU). Of these, only 25 percent test positive for cancer, but another 25 percent have false negative findings, which means the test comes back negative even though it is later found that the patient does have cancer.

New research that is expected to be presented Feb. 22 at the Multidisciplinary Prostate Cancer Symposium in Orlando, Fla., may help identify which men need a second prostate biopsy after an initial negative biopsy, the Oregon group said.

"Until now, we've really had no clear and consistent method to recommend further follow-up or diagnostic procedures for men who have a negative biopsy. We have derived a simple marker, so urologists can identify who is at risk for high-grade prostate cancer," researcher Dr. Mark Garzotto, director of urologic oncology at the Portland Veterans Affairs Medical Center and assistant professor of surgery (urology) in the OHSU School of Medicine, said in a prepared statement.

For their study, Garzotto's team studied 511 men at the veterans' center who had been referred to urology clinics for suspicion of prostate cancer. All of the men had a prior negative biopsy.

The researchers found that a high prostate specific antigen (PSA) level adjusted for prostate size was an indicator for repeat biopsy. A Gleason score of seven or above was indicative that life-threatening prostate cancer may be present and a repeat biopsy is needed.

A Gleason score grades prostate cancer tissue on a scale of 2-10, based on how it looks under the microscope. Lower Gleason scores indicate that the cancer is less likely to spread, while higher scores suggest the tumor is more likely to spread.

"What we worry about is which men may have high-grade cancer. Now, we can prescribe a second biopsy for a few months later. We know that this is a judicious use for a biopsy," Garzotto said.

Pinpointing patients who need a second biopsy will not only help identify which men may have a deadly form of prostate cancer, but it could also reduce the rate of unnecessary biopsies. This is important, since prostate biopsies are costly and can result in anxiety, pain, bleeding and infection.