Enzalutamide versus flutamide for castration-resistant prostate cancer after combined androgen blockade therapy with bicalutamide: a retrospective study

Alternative anti-androgen therapy (AAT) with flutamide after combined androgen blockade (CAB) therapy with bicalutamide for metastatic prostate cancer is common. However, no studies have compared enzalutamide without AAT with enzalutamide after AAT with flutamide as treatment for castration-resistant prostate cancer (CRPC). We aimed to compare the efficacies of flutamide and enzalutamide for CRPC. In our hospital, 55 patients were diagnosed with CRPC after CAB therapy and administered flutamide or enzalutamide between May 2014 and December 2017. Patients with flutamide failure were administered enzalutamide. We evaluated the (1) prostate-specific antigen (PSA) best response with initial therapy, (2) PSA progression-free survival with initial therapy (PSA-PFS), (3) PSA best response with enzalutamide therapy, (4) PSA-PFS of enzalutamide therapy, and (5) overall survival (OS). As first-line therapy, patients were administered enzalutamide (n = 29) or flutamide (n = 26). In the flutamide group, 18 patients showed disease progression and were administered enzalutamide. PSA best response was statistically higher in the enzalutamide group. PSA-PFS was significantly longer in the enzalutamide group [hazard ratio (HR) 0.42, 95% confidence interval (CI) 0.19–0.92, p = 0.024]. However, there was no significant difference in PSA best response with enzalutamide therapy and PSA-PFS between the first- and second-line enzalutamide therapies (HR 0.80, 95% CI 0.33–1.94, p = 0.62). There was no significant difference in OS between enzalutamide and flutamide groups (HR 1.85, 95% CI 0.53–6.42, p = 0.33). AAT with subsequent flutamide after CAB therapy with bicalutamide may be suitable for some CRPC patients.