INITIAL EXPERIENCE OF THE ENZALUTAMIDE TREATMENT FOR CASTRATION-RESISTANT PROSTATE CANCER

(Objective) Enzalutamide is an oral androgen-receptor inhibitor that prolongs survival in men with castration-resistant prostate cancer (CRPC). We retrospectively evaluated clinical efficacy and safety of enzalutamide in CRPC. (Patients and methods) We reviewed clinical records of 73 patients who had received enzalutamide for the CRPC at Showa University and affiliated 7 hospitals. Enzalutamide was given at a dose of 160 mg/day, but some patients were treated at lower dose because of there age or poor performance status. Prostrate-specific antigen (PSA) response, prior docetaxel use and the previously administered agents were evaluated retrospectively. (Results) The median patients age was 77 years, the median Gleason score was 9 and the median PSA level at baseline was 26.9 ng/ml. The patients who had prior docetaxel use were 29 (39.7%) and the median of total docetaxel dose was 460 mg/body. The median number of total prior treatments (anti-androgens, Estramustine and steroid) was 3. Twenty seven (61.4%) patients with docetaxel-naïve achieved over 50% reduction of PSA level from baseline, but only 7 (24.1%) in patients previously treated with docetaxel. The most common adverse events included fatigue (24.7%), anorexia (24.7%) and the nausea (16.4%). We found a small proportion of responders to enzalutamide experienced a PSA flare. (Conclusion) Our results of the use of Enzaltamide for CRPC were similar with previous reports. PSA flare was found in some patients with CRPC who responded to enzaltamide. It should be noted that this possible PSA flare phenomenon.