Up to now doctors couldn't tell a man much about his chances of maintaining sexual function after surgery or radiation for prostate cancer.
"We'd say about half recovered or maintained their function," says Dr. Martin Sanda of Beth Israel Deaconess Medical Center in Boston. "And we'd be able to turn that up or down a little bit based on age."
But now Sanda and colleagues around the country have provided a better crystal ball, based on measuring patients' sexual function before treatment and then two years after undergoing prostate surgery, external radiation or implants of radioactive "seeds."
The predictions are based on a study of about a thousand prostate cancer patients that appears in the current issue of the Journal of the American Medical Association.
The answers will encourage some men and discourage others, depending on the treatment they get, their age, and their pre-treatment PSA level. But at least they'll have a more realistic idea of what to expect before starting down the road.
"It helps the process of deciding and going forward," Sanda told Shots. "Because we're taking the issues out of the black box and saying 'What does this mean to you?'"
Take a man of 60 who starts out with good sexual function and a PSA level under 10. If he's eligible for so-called nerve-sparing prostate surgery, "he's looking at a 57 percent chance of recovering his erections" two years after the operation, Sanda says.
But if that 60-year-old sometimes had erectile problems before the operation, his chances of good function after surgery drops to 38 percent. And if his pre-op PSA was over 10 and he couldn't get nerve-sparing surgery – because his prostate tumor was too large – then his predicted post-op erectile function drops to only 13 percent.
One thing that's new about the data is the importance of pre-op PSA, prostate-specific antigen. It's a rough measure of two things – how large a man's prostate is, and how much cancer is present.
That a high PSA turns out to be a risk factor for post-treatment sexual function "is not a surprise, it makes sense," Sanda says, "but it's not something that had been previously described."
Overall, the study found that 40 percent of men who had their prostates surgically removed had good recovery of sexual function two years later, compared to 58 percent of men who had conventional radiation therapy and 63 percent who had brachytherapy, or radioactive seed implants.
But that doesn't mean a man who wants to preserve his sexual function should necessarily choose brachytherapy and avoid surgery.
"Men are selected for brachytherapy only if they have a PSA less than 10 and their prostate is sufficiently small for seed implants," Sanda says. "So they're on the whole a more favorable group."
In other words, other factors besides sexual outcomes enter into choosing prostate cancer treatment. For instance, some men might be wise to choose hormonal therapy to block the effect of testosterone, which fuels the growth of any cancer cells not eliminated by radiation or surgery. But that will lower his chances of sexual function.
One surprising finding: Many men aren't trying medicines or other treatments that might help them improve sexual function after prostate cancer treatment.
Very few men had tried other treatments for erectile problems, such as suppositories or injections in the penis or use of a vacuum device to achieve erection.
"It can be hard for patients to follow through with some of these measures after they've finished treatment," Sanda says. "It can be a matter of cost, or perhaps some men feel inhibited or anxious about it."