Nick Mulcahy

October 29, 2012

BOSTON, Massachusetts — Sildenafil citrate (Viagra, Pfizer) might have a role as a preventive therapy for erectile dysfunction in men who undergo radiation therapy for clinically localized prostate cancer.

In a prospective study of such men, prophylactic sildenafil was associated with significantly better erectile function scores than placebo at 2 years.

Complete loss of erections after radiation treatment occurs in 30% to 60% of men with prostate cancer, said lead author Michael J. Zelefsky, MD, who spoke during a press conference here at the American Society for Radiation Oncology (ASTRO) 54th Annual Meeting. He is from the Memorial Sloan-Kettering Cancer Center in New York City.

In current clinical practice, sildenafil (a phosphodiesterase type 5 inhibitor) and other erectile dysfunction drugs help men regain their potency in 60% to 70% of cases in which erectile dysfunction is induced by radiation therapy. But the treatment is usually administered after the development of the problem, he explained.

In this placebo-controlled study, the first of its kind, sildenafil was administered before, during, and after radiation therapy. A daily pill was given for 6 months. The men, who were blinded to their treatment, could also request sildenafil at any time (on demand).

All of the participating men had excellent baseline sexual function, Dr. Zelefsky reported.

Among 144 patients, overall self-reported erectile function scores (measured on the International Index of Erectile Function [IIEF]) were significantly higher in the sildenafil group than in the placebo 6 months (58.6 vs 49.4; P = .006), 12 months (56.3 vs 48.2; P = .02), and 24 months (54.9 vs. 47.6; P = .04) after therapy.

To be included in the study, men had to have a baseline IIEF erectile function domain score of at least 17.

The investigators decided to use sildenafil preventatively because "emerging information" from other studies suggested that the drug might have value in "penile rehabilitation," said Dr. Zelefsky. Sildenafil "may prevent the induction of impotence" and "may protect the vasculature," he said.

"The results are important," said Benjamin Movsas, MD, from the Henry Ford Hospital in Detroit, Michigan, who moderated the press conference, "because this is such an important quality-of-life issue." However, Dr. Movsas hesitated to endorse the approach. "We need to see the published data and go from there," he told Medscape Medical News.

Still, Dr. Movsas is drawn to the idea of using sildenafil preventively. "There is a potential downside to waiting," he said about the strategy of prescribing treatment after the condition emerges.

Dr. Zelefsky suggested that more research is needed to fine tune the approach. "The most significant improvements were seen at 6 and 12 months following treatment, with a slight dip at the 24-month mark, suggesting that future trials need to be conducted to demonstrate if a longer treatment duration can further improve patient outcomes," he said in a press release.

Hurricane Sandy Disrupts Plenary Session

In this study, 290 patients with clinically localized prostate cancer were treated with external-beam radiation therapy and/or permanent interstitial implantation and were randomly assigned (in a 2:1 ratio) to sildenafil 50 mg/day or placebo.

However, only 144 men were included in the topline-results analysis. These were the men who completed sexual function questionnaires before therapy and at least at 1 other time period, and who did not undergo androgen-deprivation therapy.

The study protocol originally called for radiotherapy alone to be compared with prophylactic and on-demand sildenafil before, during, and after radiotherapy in combination with or without androgen-deprivation/hormone therapy. During the press conference, Dr. Zelefsky did not explain why the topline data did not include the patients who received androgen-deprivation therapy.

The primary objective of the study was to determine whether prophylactic sildenafil could preserve erectile function.

A more complete account of the study results will be made public once the meeting's plenary session is posted online. In an unusual development, ASTRO cancelled the plenary session because of Hurricane Sandy. However, the organization recorded the presenters this afternoon, just before transportation services were officially halted in Boston. As of this writing, the recorded session has not been posted online.

Secondary objectives of this study included determining whether prophylactic sildenafil during therapy reduces the acute and late urinary effects of radiotherapy; determining the impact of dosimetry and radiation exposure to both the neurovascular bundle and bulb of the penis on erectile function preservation after brachytherapy and hormone therapy; assessing the impact on quality of life after prophylactic sildenafil; and determining the relation between testosterone levels, erectile function, and prophylactic sildenafil.

American Society for Radiation Oncology (ASTRO) 54th Annual Meeting: Abstract 3. Presented October 29, 2012.