Predicting sexual potency after prostate cancer treatment

By Deborah Kotz, Globe Staff

After contending with a diagnosis and the treatment of prostate cancer, many men also face the prospect of lifelong side effects like urinary problems and a loss of sexual function. While doctors do their best to provide patients with the rates of such side effects for any given treatment, they’re usually somewhat off base since a lot depends on the man himself -- his age, overall health, and extent of his cancer.

Now doctors may be better able to predict which men will become impotent from prostate cancer treatments, thanks to a new model developed by researchers from Beth Israel Deaconess Medical Center. The study, published yesterday in the Journal of the American Medical Association, found that several factors helped determine whether a man would develop sexual problems following treatments such as surgery, radiation, and implanted radioactive pellets. These include his level of sexual function before the treatment, his age, and the extent of his cancer as measured by his prostate specific antigen, or PSA, score.

“It’s helpful for patients to understand what the real impact will be for them down the line even if they still choose to go with the treatment that will be most likely to save their life,” said study co-author Dr. Martin G. Sanda, director of the Prostate Care Center at Beth Israel Deaconess.

The study found that the radioactive pellets or brachytherapy enabled the most men to retain their sexual function. Two years following treatment, 52 percent of the study’s participants who were able to get full erections before treatment reported having problems with erectile dysfunction after having surgical treatment; that compares with 42 percent of those who had external radiation and 37 percent who had the brachytherapy.

One limitation of the study, however, is that men chose which treatment to have and weren’t randomized to have one or the other; brachytherapy is usually reserved for men with less aggressive forms of cancer, said Sanda, which could explain the lower rate of side effects.

“Randomized trials would be helpful, but I think this is one of the strongest studies to date in this field to help patients individualize their decisions,” said Dr. Michael Barry, an internist at Massachusetts General Hospital and president of the Foundation for Informed Medical Decision Making, who wrote an editorial that accompanied the study. “It’s really where we’re headed.”

For radiation and brachytherapy, the model was able to correctly predict 87 to 90 percent of the time which men would wind up with preserved erectile function. For surgery, it predicted correctly 77 percent of the time -- possibly reflecting differences in the proficiency of surgeons to spare vital nerves necessary for sexual function.

Interestingly, obesity appeared to play a role in sexual side effects, but only in men who had the brachytherapy. “It’s a noteworthy observation that may carry interest to general public,” said Sanda. Overweight men may be inclined to shed their pounds if they’re worried about sexual dysfunction following their treatment.

Sanda and his colleagues have also developed a model for predicting urinary incontinence and difficulty with urination following prostate cancer treatments, and they expect to publish their results within the next few months. “The common thread between both models is that where a man is at baseline -- in terms of his overall health, degree of cancer, and function -- are key drivers in predicting how things will wind up after treatment.”

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