Predictors of poor response to secondary alternative antiandrogen therapy with flutamide in metastatic castration-resistant prostate cancer.

OBJECTIVE: In Japan, flutamide had been commonly used as second-line alternative antiandrogen hormonal therapy for metastatic castration-resistant prostate cancer that relapses after initial hormone therapy before new androgen pathway inhibitors became available. In this study, we attempted to identify predictive factors for efficacy of alternative antiandrogen as second-line hormone therapy. METHODS: We identified consecutive 65 patients with metastatic castration-resistant prostate cancer who were treated with alternative antiandrogen as second-line hormonal therapy (bicalutamide to flutamide). All patients were treated with combined androgen blockade initially. We analyzed correlations between progression-free survival of alternative antiandrogen and clinicopathological characteristics, including patients' ages, initial prostate-specific antigen levels, prostate-specific antigen levels at flutamide induction, Gleason scores, T stage, N stage, extent of disease grades on bone scan and previous duration of prostate cancer response to combined androgen blockade. RESULTS: In univariate analysis, T stage, N stage and previous duration of response to combined androgen blockade were correlated with shorter progression-free survival. We found four significant risk factors for shorter progression-free survival in multivariate analysis: initial prostate-specific antigen level, clinical N stage, extent of disease grades and previous duration of response to combined androgen blockade. CONCLUSIONS: Initial prostate-specific antigen, N stage, extent of disease grades on bone scan and previous duration of response to combined androgen blockade were the significant predictors for efficacy of alternative antiandrogen as second-line hormone therapy in patients with metastatic castration-resistant prostate cancer. These findings might support that decision-making of when to start the new androgen receptor pathway inhibitors.