Guidelines suggest that patients with low-risk, slow-growing prostate cancer consider keeping an eye on their cancer rather than being treated for it. City of Hope scientists, though, found that many patients classified with “very low-risk” cancer actually had higher-risk prostate cancer.

“Watchful waiting,” as it is called, often is recommended for older patients when biopsies indicate they have low-risk tumors. These patients are more likely to die from other causes than from prostate cancer, and the side effects of cancer treatment may outweigh its benefits, explained Michael Nazmy, M.D., surgical fellow in City of Hope’s Division of Urology and Urologic Oncology.

Researchers studied nearly 1,300 patients whose biopsies showed very low-risk cancer, but who received surgery. Analyzing the prostate tissue after surgery, scientists found that more than a third of these prostate cancers were more aggressive than the initial biopsies indicated.

Nazmy and his colleagues looked specifically at Gleason scores, which are determined through a pathologist’s examination of the prostate tissue for cancerous abnormalities. For prostate cancer, these scores range from 6 (low-risk cancer) to 10 (aggressive disease).

A final examination of the removed glands showed that more than 36 percent of the men actually had a Gleason score of 7 or higher. The higher score may have warranted active treatment instead of watchful waiting.

Despite the result, Nazmy said most of the patients have good postsurgical outcomes, with more than 90 percent surviving five years after surgery.

“Our study examined only patients who underwent surgery, so it is unknown if these positive results would hold true if there was no intervention,” Nazmy said. “Further studies and longer follow up are needed to compare survival rates of patients who chose surgery versus those who did not, and whether diagnostic guidelines or treatment recommendations need to be revised if there is a disparity.”

Nazmy presented the study findings at the American Urological Association 2012 Annual Meeting in Atlanta.