CHICAGO (FRONTLINE MEDICAL NEWS) – Androgen deprivation therapy (ADT) combined with radiation therapy can safely be reduced from 36 to 18 months without compromising outcomes or quality of life in patients with high-risk localized prostate cancer, according to the final results of a randomized phase III trial.

At a median of 9.4 year follow-up of 630 patients who were randomized to receive pelvic and prostate radiotherapy combined with either 36 or 18 months of ADT, the 10-year overall survival rate was 62.4% and 62.0% in the treatment arms, respectively (global hazard ratio, 1.024), Abdenour Nabid, MD, reported at the annual meeting of the American Society of Clinical Oncology.

Disease-free survival was 44.5% and 39.2% in the groups, respectively (HR, 0.835). This difference did not reach statistical significance, said Dr. Nabid of Centre Hospitalier Regional Universitaire, Sherbrooke, Quebec, Canada.

The disease-free survival curves separated over the course of the study, mainly because of a significant difference in biochemical failure between the groups, which favored the 36-month arm (24.8% vs. 31.0%; HR, 0.714), but this is not an unexpected finding with longer treatment, he explained.

“Does this biochemical control give you more control of the disease? I’m not sure,” he said, noting that bone metastases alone occurred in 23 and 24 patients in the 36 and 18 month treatment groups, respectively, and bone plus other site metastases occurred in 11 patients in each group. “At the end of the day, the P value (for disease-free survival) is not significant (.0768).”

Further, a quality of life analysis showed that patients in the 18-month treatment arm performed significantly better on 6 of 21 scales and 13 of 55 items addressing various quality of life factors. On two of these items – hot flushes and enjoyable sex – a clinically relevant difference of 10 or more points in mean scores was noted, he said.

Long-term ADT combined with radiotherapy is a standard treatment for patients with high-risk prostate cancer, but the optimal duration of treatment has not been defined, Dr. Nabid said.

The current trial looked at treatment duration in patients 80 years and younger (median of 71 in both groups) with T3-T4 disease, PSA levels greater than 20 mg/ml, and Gleason score greater than 7, with normal hepatic function and no regional disease or distant metastases. ADT included a 50 mg initial dose of bicalutamide daily for 1 month plus 10.8 mg of subcutaneous goserelin every 3 months, as well as pelvic and prostate radiotherapy.

On both univariate and multivariate analyses including age, Gleason score greater than 7, treatment duration, prostate-specific antigen greater than 20, T3-T4 disease, and biochemical failure during follow-up, only age and Gleason score were significantly associated with overall survival (HR, 1.05 for age in both analyses, and 1.40 and 1.42, respectively for Gleason score greater than 7 on univariate and multivariate analyses).

“In localized high-risk prostate cancer treated with radiotherapy and androgen deprivation therapy, androgen deprivation therapy duration can be safely reduced from 36 to 18 months,” Dr. Nabid said, adding that 18 months could represent a threshold effect in ADT duration and that side effects and treatment costs can be reduced with shorter duration of therapy.

“Eighteen months of ADT represents a new standard of care,” he concluded.

This study was funded by AstraZeneca Pharmaceuticals. Dr. Nabid has been a speaker, advisory board member, and/or received financial support from Janssen Canada, Sanofi, Astellas, and Bayer.