The objective of this study is to compare the efficacy and safety of enzalutamide or alternative AA therapy in CRPC participants who were previously treated with a combined androgen blockade therapy which included bicalutamide (Bic-CAB). Efficacy and safety of enzalutamide and alternative AA therapy will be evaluated, and effective therapy against CRPC after treatment with Bic-CAB will be investigated.

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