For men having prostate cancer surgery, one of the biggest fears is that they will be left impotent. Unfortunately, the research that might help address that question is likely only to confuse.

A notable study in 2005 showed that a year after surgery, 97 percent of patients were able to achieve an erection adequate for intercourse. But last month, researchers from George Washington University and New York University reviewed interim data from their own study showing that fewer than half of the men who had surgery felt their sex lives had returned to normal within a year.

So which of the studies is right? Surprisingly, they both are.

The results depend on several crucial variables - the type of patient studied, sex life before surgery and, most important, the definitions doctors use to define potency.

Of the 219,000 men a year who receive diagnoses of prostate cancer, nearly half undergo surgical removal of the gland, according to the National Cancer Institute. Most top surgeons report that an overwhelming majority of their patients can achieve erections “adequate for intercourse” after the operation. (Candidates for surgery often shop on the Internet for the surgeons who post the best scores.)

Under that definition, a man who had regular sex after surgery, a man who managed to have sex only once and a man who struggled mightily each time he had sex would all be considered success stories.

“That definition is misleading,” said Dr. Jason D. Engel, director of the urologic robotic surgery program at the George Washington University Hospital. “It doesn’t mean it was good intercourse, and it doesn’t even mean your penis was hard. That man is going to say, ‘I’m impotent.’ But in the surgeon’s eyes, that man had an erection adequate for intercourse.”

The better question for men is whether they can have sex when they want to, with or without drugs like Viagra. In a recent series of patients, Dr. Engel found that after a year 47 percent of men who had robotic prostatectomy were able to have regular sex.

Although he could cite statistics to give men a more hopeful view, he said that did not help the patient.

“I know what a patient wants to know, and I know what he’s scared about,” he said. “I think I have a lot happier patients, because they know the reality.”

The reality is that whether a man is able to have sex after prostate surgery depends as much on the man as it does on the surgeon. How good was his sex life before cancer? Does he have a supportive partner? Did he need to use an erection drug before surgery?

Dr. Ash Tewari, director of robotic prostatectomy at New York-Presbyterian/Weill Cornell Medical Center and a co-author of the study in The Journal of Urology, said the 97 percent potency data in the report was from a “select” group.

“It’s a very crude definition, I totally agree,” said Dr. Tewari, who will perform about 600 procedures this year, one of the most prolific totals in the nation.

If a patient has good sexual function without erection-enhancing drugs before surgery, Dr. Tewari tells him that he has about an 85 percent chance of regaining an erection firm enough for intercourse, although he may need erection drugs and it may take up to 18 months for his function to return.

This all depends on whether the cancer is early, away from nerves and contained. “The patient should not forget why they are getting this treatment,” Dr. Tewari said. “Keeping that focus in mind, can we do something to get sexual function back? Yes, but it depends on the cards we are dealing.”

Men who are older or who used erection drugs before surgery have a more difficult recovery. After surgery, patients undergo penile rehabilitation, which involves regular use of the drugs, even if the man is not having sex. The goal is to increase blood flow that will bathe damaged tissue and promote healing. After surgery, many patients will always need drugs, injections or other treatments to have sex, said Dr. Andrew McCullough, director of the Sexual Health and Male Infertility and Microsurgery Programs at N.Y.U.

  “Less than 5 percent of patients are as good as they were before surgery,” he said. “The one thing you’re going to be facing, regardless of what people tell you, is erectile dysfunction. But the good news is that it is eminently treatable. If you accept the fact that you’re going to have it, and you address it early on, you shouldn’t skip a beat.”

One obvious change for a man after surgery is that he no longer ejaculates fluid. Many men also complain that the quality of their orgasms changes. In 2004, Dr. McCullough presented an abstract to the American Urological Association that asked 230 consecutive patients before surgery to rate orgasm quality. Two years after surgery, they were asked again, and 53 percent who had good or very good orgasms before surgery said the quality had declined.

Some men complain that their penis is smaller after surgery. The data are mixed, but it appears less of an issue with robotic surgery. The results may be explained by different methods of measuring penile length at different medical institutions.

Then there are those fortunate men who also have quick recoveries and resume normal sex lives. One of them is Gerald Anthony of Freeport on Long Island, a 59-year-old retired New York City police officer who had prostate cancer surgery with Dr. Tewari in December. Already, Mr. Anthony said, his sexual ability is as good as it was before, and he does not require medication, though he agrees that orgasm is different now.

“I’m still happy,” he said. “I hear a little trumpet section, but I don’t hear the whole orchestra.”

His case also illustrates something that does not turn up in many of the medical studies.

“Having a beautiful wife - that also helps,” said Mr. Anthony, who has been married for 19 years. “My wife is better than any Viagra.”

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New York Times
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