Tolerability, efficacy and pharmacokinetics of bicalutamide 300 mg, 450 mg or 600 mg as monotherapy for patients with locally advanced or metastatic prostate cancer, compared with castration.

Objective: To evaluate the pharmacokinetics, tolerability and effect on endocrinology of bicalutamide given as once-daily monotherapy at doses of >150 mg to patients with locally advanced (M0) or metastatic (M1) prostate cancer, with efficacy as a secondary endpoint.

Patients And Methods: Patients were initially enrolled to receive bicalutamide 300 mg in a non-randomized phase, after which further patients were randomized to higher bicalutamide doses (in 150 mg increments) or castration. Overall, 248 patients received bicalutamide at 300 mg (21), 450 mg (95) or 600 mg (42), or castration (90).

Results: Systemic exposure to bicalutamide stabilised at a dose of approximately 300 mg, as determined by pharmacokinetic analysis. The tolerability of high doses of bicalutamide was similar to that of the 150 mg dose, with no increase in the incidence of adverse events. Patients receiving bicalutamide had early increases in the mean levels of oestradiol, testosterone and luteinizing hormone, which were maintained throughout the study. Levels of these hormones rapidly decreased in the castration group and remained low. From baseline (first day of treatment) to 12 weeks there was an equivalent reduction in prostate-specific antigen (PSA) levels across all four groups. At a median follow-up of 5 years, there was no significant survival difference between patients who received bicalutamide and those who received castration, either in M0 or M1 disease.

Conclusion: The low median PSA level (180 ng/mL) of patients with M1 disease might account for the lack of survival difference between the treatment groups. Further studies are needed to assess whether high-dose bicalutamide monotherapy can provide equivalent efficacy to castration in patients with M1 prostate cancer.