A Safety and Efficacy Study of Oral MDV3100 in Chemotherapy-Naive Patients With Progressive Metastatic Prostate Cancer

Randomized, Double Blind Treatment Period:

Inclusion Criteria:

   - Histologically confirmed adenocarcinoma of the prostate without neuroendocrine
   differentiation or small cell features

   - Ongoing androgen deprivation therapy with a GnRH analogue or bilateral orchiectomy

   - Progressive disease despite androgen deprivation therapy as defined by rising PSA
   levels or progressive soft tissue or bony disease

   - No prior treatment with cytotoxic chemotherapy

   - Asymptomatic or mildly symptomatic from prostate cancer

Exclusion Criteria:

   - Severe concurrent disease, infection, or co-morbidity that, in the judgment of the
   Investigator, would make the patient inappropriate for enrollment

   - Known or suspected brain metastasis or active leptomeningeal disease

   - History of another malignancy within the previous 5 years other than curatively
   treated non-melanomatous skin cancer

Open-Label Treatment Period:

The following inclusion criteria apply to patients receiving enzalutamide or placebo during
double-blind treatment.

Eligible patients must meet all inclusion criteria.

   - Received randomized double-blind treatment in PREVAIL;

   - Open-label day 1 visit is within 6 months after this amendment is approved and becomes
   effective at the study site;

   - Is willing to maintain androgen deprivation therapy with a gonadotropin-releasing
   hormone (GnRH) agonist/antagonist or has had a bilateral orchiectomy;

The exclusion criteria apply only to patients starting new treatment with enzalutamide
after receiving placebo as randomized treatment. Each patient must not meet any of the
following criteria:

   - Has taken commercially available enzalutamide (Xtandi);

   - Severe concurrent disease, infection, or co-morbidity that, in the judgment of the
   Investigator, would make the patient inappropriate for enrollment

   - Known or suspected brain metastasis or active leptomeningeal disease