Does radiation after the removal of a cancerous prostate gland reduce a man's risk of subsequent cancer spreading to other parts of the body? The question was at the heart of a landmark, multicenter study by the Southwest Oncology Group, one of the largest cancer clinical trials cooperative research networks in the United States.
The results, published in the Nov. 15 edition of the Journal of the American Medical Association, showed a reduction in the metastasis of cancer — extending the time to metastasis from 13.2 to 14.7 years — a difference that was not considered statistically significant. Study authors, including Public Health Science Division's Dr. Catherine Tangen, did find that radiation reduced the risk of prostate-cancer recurrence by about 40 percent.
Additionally, researchers found that men who had a low prostate-specific antigen (PSA) level after surgery and who received radiation had a significantly lower risk of subsequent development of a measurable PSA after surgery — a sign of possible cancer recurrence. PSA is a blood test that checks for a protein secreted by normal and cancerous prostate cells. When the prostate has been removed and the PSA level in the blood rises, it is generally a signal that cancerous cells are still present and growing.
The researchers studied 425 men from 1988 through 1997, and continued to follow their health for long-term analysis through September 2005. All the men in the study had surgery to remove their prostate gland and were found to be at a higher risk of cancer recurrence based on the extent of their cancer. The men were then randomly selected to receive either radiation or observation only during the study; 214 men in the group received radiation and 211 did not.
In the radiation group, 35.5 percent of the 214 patients were diagnosed with metastatic prostate cancer or died from any cause compared to 43 percent of the 211 patients in the observation group. Although no statistically significant improvement in survival was achieved, there were 83 deaths and a median survival of 14.7 years for the radiation group and 71 deaths in the observation-only group with a median survival of 13.8 years.
The study also found that there were more adverse events in the radiation group (23.8 percent) versus the no-radiation group (11.9 percent). Adverse events included rectal complications, urethral stricture and total urinary incontinence.
"Adjuvant radiation clearly reduces the risk of local recurrence," Tangen said. "An obvious follow-up question is whether radiation therapy can be as effective if it is delayed until the PSA increases, thereby targeting the men at greatest risk."
Each year, approximately 230,000 men are diagnosed with prostate cancer. According to the American Cancer Society, it is the second most common type of cancer in American men and the third leading cause of cancer death for men.