Mathematical models that are based on patient characteristics, pretreatment sexual functioning, and treatment details help predict whether men will have erectile function 2 years after therapy for early-stage prostate cancer, according to a report in the Sept. 21 issue of JAMA.
The predictive models were developed in a cohort of 1,027 patients who underwent prostatectomy, external beam radiotherapy, or brachytherapy during 2003-2006, and they were then validated against actual experience in a separate registry of 1,913 community-based patients.
This verification "suggests that these findings are generalizable and may help physicians and patients to set personalized expectations regarding prospects for erectile function in the years following primary treatment for prostate cancer," said Dr. Mehrdad Alemozaffar of the division of urology at Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, and his associates (JAMA 2011;306:1205-1214).
The investigators developed their models using data from a prospective, longitudinal cohort of men who were treated at nine university-affiliated hospitals. A total of 524 elected to undergo prostatectomy, 241 opted for external beam radiotherapy, and 262 had brachytherapy for their clinical stage T1 or T2 prostate cancer.
Before treatment commenced, 28% of the prostatectomy group, 47% of the radiotherapy group, and 33% of the brachytherapy group reported that they already had some erectile dysfunction. At 2 years after treatment, these rates increased to 65%, 63%, and 57%, respectively.
For prostatectomy, four factors – younger age, lower PSA level at baseline, better pretreatment sexual functioning, and nerve-sparing surgery – were found to raise the odds that the study subjects would be able to attain functional erections suitable for intercourse 2 years after treatment. "Erectile function increased approximately linearly with decreasing age and with increasing pretreatment sexual functioning score," Dr. Alemozaffar and his colleagues said.
Using these data, they constructed a table of probabilities that men choosing prostatectomy would be able to attain functional erections. For example, a 50-year-old man’s prospects for having functional erections after prostatectomy will vary between 6% and 70% depending on his pretreatment sexual function score, his baseline PSA level, and whether he planned to use a nerve-sparing surgical technique.
For subjects having external beam radiotherapy, the odds that they will be able to attain functional erections suitable for intercourse improve with lower PSA level, better pretreatment sexual functioning, and no use of neoadjuvant hormone therapy. According to the model, a patient’s probability of recovering the ability to attain functional erections varies between 16% and 92%, depending on these three factors.
For those having brachytherapy, the factors associated with better odds of attaining functional erections are better pretreatment sexual functioning, younger age, black race, and lower body mass index. For example, a 60-year-old man’s probability of doing so varies from 11% to 98%, depending on his pretreatment sexual functioning, age, race, and BMI.
Dr. Alemozaffar and his associates assessed how their models performed in a separate cohort of 1,913 men enrolled in a community-based registry. The model-predicted probabilities corresponded well to the observed outcomes in this cohort.
Thus, the models provide "a validated, broadly applicable framework to predict the probability of long-term posttreatment erectile dysfunction for individual patients," they said.
It was notable that in initial univariate analyses, poorer recovery of erectile function correlated with higher numbers of comorbid conditions. However, this correlation did not persist in multivariate analyses, so the models do not include comorbidities.
"Other researchers have found diabetes and peripheral vascular disease to be associated with worse posttreatment sexual outcome," but those studies did not adjust for differences in pretreatment sexual function. It thus appears that pretreatment sexual function may supersede the effects of comorbidities on posttreatment erectile function, they said.
Also of note was the finding that the models were more accurate at predicting erectile function after external radiotherapy than after prostatectomy. The reason for this difference is not yet known, and it is possible that surgical factors, such as the surgeon’s proficiency or variations in specific techniques, "may contribute to a broader range of outcomes" after prostatectomy than after radiotherapy. This issue warrants further study, they added.
This study was supported by the National Institutes of Health. Dr. Alemozaffar’s associates reported ties to numerous industry sources.