Earlier research had estimated that ED affects a wide range of patients, from about 20% to 88%. To help clarify the risk for patients, Timothy Siegel, MD, from the Center for Prostate Disease Research in Rockville, Md., and his colleagues, compared erectile function in patients receiving three different treatment types:

• radical prostatectomy -- removal of the entire prostate gland;
• external beam radiation -- radiation therapy administered in a manner similar to an X-ray; and
• watchful waiting -- keeping an eye on the cancer, but giving no immediate treatment unless it starts to grow more rapidly.

The researchers collected data on more than 800 prostate cancer patients, 69% of whom reported normal erectile function before treatment. They found that at an average of 53 months after treatment, just 10% of patients receiving radical prostatectomy and 15% of those treated with external beam radiation had normal erectile function. In contrast, 38% of the men who chose watchful waiting had adequate erections after six months. Overall, more than 80% of the men who were treated developed ED during the study, regardless of their age.

"Patients who elect non-nerve sparing radical prostatectomy or external beam radiation therapy should expect a high incidence (greater than 85%) of erectile dysfunction after therapy," note the study authors. "In our experience, erectile dysfunction did not develop based on the type of therapy received, but whether a patient received active therapy for prostate cancer."

In a related editorial, Ian M. Thompson, Jr., MD, of the University of Texas Health Sciences Center in San Antonio, points out that these findings show "erectile dysfunction is common in all men after diagnosis of prostate cancer, whether treated with surgery or radiation, or even if they choose surveillance alone."

Kenneth J. Pienta, MD, director of urologic oncology at the University of Michigan Comprehensive Cancer Center, says that these findings are not really a surprise. "They fit already published data that demonstrate that the majority of men who undergo therapy for prostate cancer with a radical prostatectomy or radiation therapy have erectile dysfunction afterwards. This should be the expectation going into treatment, and men should understand the side effects of therapy before starting it," says Pienta, who is an expert adviser on prostate cancer to the American Cancer Society.

All treatments for localized prostate cancer carry similar risks for erectile dysfunction, Pienta says. "Younger, thinner men tend to have less dysfunction then older men, but each person is a unique individual and everyone''s results vary," he says. "The important thing is to identify and treat cancer that needs to be cured."