Final results of the Canadian prospective phase II trial of intermittent androgen suppression for men in biochemical recurrence after radiotherapy for locally advanced prostate cancer

Abstract

This prospective Phase II study was undertaken to evaluate intermittent androgen suppression as a form of therapy in men with localized prostate cancer who failed after they received external beam irradiation. Patients who demonstrated a rising serum prostate-specific antigen (PSA) level after they received radiotherapy and who were without evidence of distant metastasis were accepted into the study. Treatment in each cycle consisted of cyproterone acetate given as lead-in therapy for 4 weeks, followed by a combination of leuprolide acetate and cyproterone acetate, which ended after a total of 36 weeks. Of 109 patients registered, 103 patients were eligible for interruption of treatment, yielding a PSA response rate of 95%. The study continued for 6 years with a mean follow-up of 3.7 years (median follow-up, 4.2 years). The time off treatment averaged 53% of the total cycle time but, in absolute terms, decreased with each succeeding cycle, ranging from 63.7 weeks in Cycle 1 to 25.6 weeks in Cycle 5. Prostate volume was reduced by 40% in Cycle 1 and by 34% in Cycle 2, and there were no decreases in Cycle 3 or Cycle 4. At the end of the trial, 38.5% of patients still were receiving treatment, 23.9% of patients had failed, and 15.6% of patients had died. Only 2% of deaths were cancer-specific. Biochemical recurrence after irradiation for localized prostate cancer was amenable to cyclic androgen withdrawal therapy and showed a high response rate. Despite progressively shorter treatment cycles, the off-treatment interval remained appreciable, ranging from 65% in Cycle 1 to 46% in Cycle 5.