A man facing prostate cancer treatment can now get a rough sense of his odds of becoming impotent after the procedure, researchers said Tuesday.

Doctors currently don't have good numbers to give to patients wanting to know their individual risk of side effects, such as erectile dysfunction or incontinence, that can take a big toll on quality of life.

The new study, published in the Journal of the American Medical Association, provides formulas to help gauge those risks for three common types of treatment, including surgery and radiation.
One expert called the findings "a major step forward," but also warned patients and doctors not to use the results to choose between different types of treatment.

"It's really at this stage for the patient who has made up his mind that he's going to have surgery or radiation and then asks, What can I expect?" said Dr. Philipp Dahm, a urologist from the University of Florida in Gainesville who wasn't part of the study.

"This will give you a very good answer," he told Reuters Health.

According to the American Cancer Society, one in six men gets prostate cancer at some point in his life, and one in 36 dies from the disease.

There is controversy over how to treat low-risk tumors, which often don't cause any harm if left untreated. But when the disease is more advanced, surgery and radiation are common options.

This year, for instance, about 90,000 Americans will undergo radical prostatectomy, a procedure in which the entire prostate is removed. They face common side effects such as impotence and incontinence during routine activities, and urologists have recently learned that some may also leak urine during sex.

Getting useful information about how common these problems are is not easy, however.

In the new study, researchers used data from more than 1,000 men treated for prostate cancer at different hospitals across the country. All of the participants answered questions about their sex life before being treated with prostate surgery, external radiation or radioactive "seeds" implanted in the prostate.

More than a quarter of the men said they were impotent before they were treated. Of those who weren't, 52 percent reported new erectile problems two years after their treatment.

In the surgery group, 60 percent of men who used to have a good sex life said they had become impotent. That figure was 42 percent among patients who received external radiation and 37 percent among those who had seeds implanted.

However, the chance of sexual problems varied a lot, depending on factors like age, race, weight, prior sexual function, blood levels of prostate specific antigen (PSA), hormone treatment and the specific kind of surgery.

For a normal-weight, 60-year-old African American with a good sex life, the chance that he would lose his ability to get an erection after having seeds implanted was only two percent, for example.

An extremely obese 70-year-old white man getting the same therapy would have a 58-percent risk of becoming impotent.

"Sexual function is one of the things that are most commonly affected by prostate cancer treatment," said. Dr. Martin G. Sanda, who heads the Prostate Center at Beth Israel Deaconess Medical Center in Boston and led the new study.

"Putting these formulas out there is really step one," he told Reuters Health. "Up to now there hasn't been something like this out there for side effects from prostate cancer treatment."

The next step is to make the formulas easily available, for instance as a web tool, and expand them to other side effects such as incontinence, Sanda added.

He said the information necessary to calculate a man's risk isn't hard to get, and filling out the questionnaire would only take minutes.

His group also tested its predictions in a separate group of patients and found they held up well, although the individual risk estimates come with some uncertainty.

"In general for the surgical treatment the error bars might be a little broader, as much as 20 or 30 percent, than for some of the radiation groups," Sanda said. "There is some variability, meaning there are some things that influence the outcome that may not be accounted for in the models."

In an editorial, Dr. Michael J. Barry of Massachusetts General Hospital in Boston notes that the new formulas have some important limitations.

"First, this study is observational, and patients should use the findings cautiously to help choose among treatments," he writes.

Barry also notes that a wait-and-see approach, instead of rushing to treatment, might in fact be the best way to minimize the risk of side effects while maximizing survival chances.

Dahm added that it is also important to look at other issues before choosing how to manage the disease, including cancer control and urinary problems.

"When patients make the decision they ideally should incorporate all these dimensions in their decision making," he said.

Nonetheless, he said he would use the new study when counseling patients.

"It provides the best available evidence out there," Dahm concluded.