Only 10 percent of men treated for early prostate cancer could sustain an erection sufficient for sex 15 years later, said researchers who found impotence rates were the same whether the treatment was surgery or radiation.

While surgery patients had higher impotence rates two years after treatment, by 15 years erection failure "was nearly universal" with both treatments, according to the study in the New England Journal of Medicine. The finding adds to the controversy over whether doctors treat men with early prostate cancer too aggressively.

"We are starting to realize we are over-treating this disease," said David Penson, an urologist at Vanderbilt University Medical Center in Nashville, Tenn., and a senior author on the study. Some low-risk patients with prostate cancer "don't need treatment," he said.

More than 238,000 American men are diagnosed with prostate cancer each year, and more than 29,000 die from it, making it the second leading cause of cancer death in men, according to the American Cancer Society. Most cases are discovered before the cancer spreads. In those cases, patient survival is almost 100 percent over five years.

--BLOOMBERG NEWS