An open-label, phase 2 trial of bicalutamide dose escalation from 50 mg to 150 mg in men with CAB and castration resistance. A Canadian Urology Research Consortium Study.

BACKGROUND: Bicalutamide is a widely used, relatively non-toxic anti-androgen, particularly when used in combination with androgen deprivation. In men on combined androgen blockade (CAB), the typical dose is 50 mg per day. For men receiving monotherapy with bicalutamide anti-androgen, the dose is 150 mg per day. The objective was to determine the PSA response rate to increasing bicalutamide to 150 mg per day in men who develop castrate-resistant prostate cancer (CRPC) on CAB with goserelin acetate and bicalutamide 50 mg per day.

METHODS: A national, multicentre, phase 2, open-label study in men on CAB with a rising PSA>2.0. The primary end point of the trial was PSA response at 12 months, defined as a decline by 50% or more compared with baseline value. Partial response was defined as a PSA decline of 10-49%. Secondary end points were duration of PSA response, change in slope of serum PSA, change in ratio of free PSA: total PSA at 3 months, 6 months and 12 months as compared with baseline; duration of the bicalutamide withdrawal response after discontinuation; the rate of cardiovascular events; and toxicity. The study was initially planned to accrue 100 patients, but was closed early due to diminishing accrual.

RESULTS: Sixty-four patients were accrued; 61 patients received trial treatment and constituted the intention-to-treat (ITT) cohort. 70% were M0. Among 59 evaluable ITT patients, 13 (22%) patients had a >50% PSA decline, 5 (8%) had a decline between 10 and 50%, 4 (7%) had stabilization and 37 (63%) had PSA progression. The median duration was 3.7 months (95% confidence interval of 0.92-6.21 months).

CONCLUSION: In patients with early biochemical failure on CAB with bicalutamide 50 mg, an increase in dose to 150 mg of bicalutamide resulted in a PSA response of ⩾ 50% in 22% of patients. Toxicity was mild. Bicalutamide dose intensification may benefit a subset of patients with CRPC. We believe this relatively inexpensive approach warrants further evaluation.