Nick Mulcahy

September 23, 2013

ATLANTA — In a finding that surprised the investigators of a major clinical trial, a shorter duration of hormone therapy before radiation treatment resulted in disease-specific survival comparable to that seen with a longer duration in intermediate-risk prostate cancer patients.

The 10-year disease-specific survival rate was roughly the same (about 95%; P = .45) for the 752 men who received 8 weeks of preradiation total androgen suppression (TAS) and the 728 men who received 28 weeks of the same neoadjuvant regimen.

All of the men were subsequently treated with radiation and concurrent TAS, which consisted of an additional 8 weeks of the same hormone therapy regimen.

These results come from the Radiation Therapy Oncology Group (RTOG) 9910 trial, and were reported here today at the American Society for Radiation Oncology (ASTRO) 55th Annual Meeting.

The trial had a median follow-up of 9 years and involved 152 centers in the United States and Canada. "These were not the outcomes that were expected," said lead author Thomas Pisansky, MD, from the Mayo Clinic in Rochester, Minnesota, during a meeting press conference.

He explained that the results defied a general "precedent" in cancer research — that increasing the amount of a successful treatment produces a subsequent "incremental benefit." Previous studies established short-term TAS followed by radiotherapy plus concurrent TAS as the standard of care for patients with intermediate-risk prostate cancer, Dr. Pisansky noted.

However, in this case, adding more hormone therapy was not beneficial.

"It is quite clear to us," said Dr. Pisansky, that preradiation "neoadjuvant androgen suppression need last no longer than 8 weeks."

 
We have now established conclusively where the ceiling is.
 

"We have now established conclusively where the ceiling is for the duration of androgen suppression [in intermediate-risk disease]," he added.

The outcomes are "very, very positive," he noted, referring to the fact that only about 5% of participants in the 2 study groups had died from their prostate cancer at 10 years. There was also comparable locoregional control at 10 years in the 8-week and 28-week groups (6% vs 4%; P = .07).

"There is very little room for improvement," said Dr. Pisansky about the treatment strategy, prostate cancer-related deaths, and disease control.

What about managing these men with active surveillance?

Dr. Pisansky rejected that idea, saying that men in this intermediate-risk category with a life expectancy of 10 or more years should be treated.

ASTRO president-elect Bruce Haffty, MD, from the Rutgers Cancer Institute of New Jersey in New Brunswick, who moderated the press briefing, agreed. "Intermediate-risk prostate cancer is treated for the most part," he said.

However, some men with intermediate-risk disease are managed with active surveillance at the University of California, San Francisco, as reported by Medscape Medical News.

Although the 2 treatment groups in the new study had comparable outcomes, the 28-week treatment group had more treatment-related adverse effects, Dr. Pisansky pointed out.

For instance, hot flashes and erectile dysfunction were more common in the 28-week group, according to press materials.

Study Details

Men with intermediate-risk disease were accrued in the study from 2000 to 2004.

Table. Combinations of Factors Constituting Intermediate-Risk Prostate Cancer in RTOG 9910

Tumor Stage Gleason Score PSA (ng/mL)
T1b–4 2–6 10–100
T1b–4 7 <20
T1b–1c 8–10 <20

 

The majority of the participants had T1b–2 (94%), a Gleason score above 6 (73%), and a prostate-specific antigen (PSA) level above 10 ng/mL (53%), Dr. Pisansky reported. The average age at enrollment was 71 years.

The study design called for men to be randomized to either 8 or 28 weeks of total androgen suppression with luteinizing-hormone-releasing hormone agonist plus a daily nonsteroidal antiandrogen (bicalutamide or flutamide) prior to radiotherapy and concurrent androgen suppression for 8 more weeks. The radiotherapy consisted of 70.2 Gy delivered in 39 fractions.

In the 8-week group, there were 30 prostate cancer deaths and a 10-year disease-specific-survival rate of 95%; in the 28-week group, there were 24 deaths and a 10-year rate of 96% (hazard ratio [HR], 0.81; P = .45).

There were another 200 deaths not attributed to prostate cancer or of unknown cause in the 8-week group and a 10-year overall survival rate of 66%, and another 196 deaths in the 28-week group and a 10-year overall survival rate of 67% (HR, 0.95; P = .62).

The 10-year rate of disease-free survival was 24% in the 8-week group and 23% in the 28-week group (HR, 0.96; P = .47).

The 10-year cumulative incidence of clinical and biochemical relapse in the 8-week group was 57% and in the 28-week group was 60% (HR, 1.01; P = .84).

This trial was supported by the National Cancer Institute. Coauthor Dr. Amin reports a financial relationship with Amgen, and coauthor Dr. Sandler reports a financial relationship with Astellas. Dr. Haffty has disclosed no relevant financial relationships.

American Society for Radiation Oncology (ASTRO) 55th Annual Meeting: Abstract 1. Presented September 23, 2013.

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