Comparative Study of Alternative Antiandrogen (AA) Therapy and Early Initiating of Enzalutamide for Castration-resistant Prostate Cancer (CRPC) After Combined Androgen Blockade (CAB) Therapy.

Inclusion Criteria: * Testosterone of less than 50 ng/dL * Participants who was detected of disease progression on image or relapse of PSA (All PSA values measured 3 time at least one week interval are consecutively increased and final value is 2 ng/mL or more. If third value is not higher than second one, fourth measurement will be undertaken and its value must be higher than second one.) * Participants who relapsed after CAB with bicalutamide * Eastern Cooperative Oncology Group (ECOG) performance status is 0 or 1 * Aged 20 years or older * Participants who provided written informed consent Exclusion Criteria: * Any prior treatment with enzalutamide, flutamide, abiraterone or chemotherapy, except for neoadjuvant therapy * With active double cancer * Any prior treatment with bicalutamide within 6 weeks * Participants who received systemic biological therapy (except for existing approved drug for bone or treatment with luteinizing hormone-releasing hormone (LHRH) analogue) or received treatment with other antitumor agent for prostate cancer * With serious complication * History of hypersensitivity to enzalutamide or any other excipient of enzalutamide * History of hypersensitivity to flutamide-containing agent * With liver dysfunction * Participants who are considered as inadequate by the investigator