A Study of Atezolizumab (Anti-PD-L1 Antibody) in Combination With Enzalutamide in Participants With Metastatic Castration-Resistant Prostrate Cancer (mCRPC) After Failure of an Androgen Synthesis Inhibitor And Failure of, Ineligibility For, or Refusal of a Taxane Regimen
A Study of Atezolizumab (Anti-PD-L1 Antibody) in Combination With Enzalutamide in Participants With Metastatic Castration-Resistant Prostrate Cancer (mCRPC) After Failure of an Androgen Synthesis Inhibitor And Failure of, Ineligibility For, or Refusal of a Taxane Regimen
This Phase III, multicenter, randomized, open-label study will evaluate the safety and
 efficacy of atezolizumab (anti-programmed death-ligand 1 [anti-PD-L1] antibody) in
 combination with enzalutamide compared with enzalutamide alone in participants with mCRPC
 after failure of an androgen synthesis inhibitor (e.g., abiraterone) and failure of,
 ineligibility for, or refusal of a taxane regimen. Participants will be randomized to one of
 the two treatment arms (atezolizumab in combination with enzalutamide, and enzalutamide
 alone) in a 1:1 ratio (experimental to control arm) in global randomized phase. Participants
 will receive treatment until investigator-assessed confirmed radiographic disease progression
 per Prostate Cancer Working Group 3 (PCWG3) criteria or unacceptable toxicity.
Inclusion Criteria:

 -  Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

 -  Life expectancy greater than or equal to (>/=) 3 months

 -  Histologically confirmed adenocarcinoma of the prostate

 -  Known castrate-resistant disease with serum testosterone level less than or equal to
 (</=) 50 nanograms per deciliter (ng/dL) with prior surgical castration or ongoing
 androgen deprivation for the duration of the study

 -  Progressive disease prior to screening by PSA or imaging per PCWG3 criteria during or
 following the direct prior line of therapy in the setting of medical or surgical
 castration

 -  One prior regimen/line of a taxane-containing regimen for mCRPC or refusal or
 ineligibility of a taxane-containing regimen

 -  Progression on a prior regimen/line of an androgen synthesis inhibitor for prostate
 cancer

 -  Availability of a representative tumor specimen from a site not previously irradiated
 that is suitable for determination of programmed death-ligand 1 (PD-L1) status via
 central testing

 -  Adequate hematologic and end organ function

 Exclusion Criteria:

 -  Prior treatment with enzalutamide or any other newer hormonal androgen receptor
 inhibitor (e.g., apalutamide, ODM-201)

 -  Treatment with any approved anti-cancer therapy, including chemotherapy,
 immunotherapy, radiopharmaceutical or hormonal therapy (with the exception of
 abiraterone), within 4 weeks prior to initiation of study treatment

 -  Treatment with abiraterone within 2 weeks prior to study treatment

 -  Structurally unstable bone lesions suggesting impending fracture

 -  Known or suspected brain metastasis or active leptomeningeal disease

 -  Major surgical procedure other than for diagnosis within 4 weeks prior to initiation
 of study treatment or anticipation of need for a major surgical procedure during the
 course of the study

 -  Active or history of autoimmune disease or immune deficiency

 -  Prior allogeneic stem cell or solid organ transplantation

 -  History of idiopathic pulmonary fibrosis, organizing pneumonia (e.g., bronchiolitis
 obliterans), drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of
 active pneumonitis on screening chest computed tomography (CT) scan

 -  Positive human immunodeficiency virus (HIV) test, active tuberculosis, active
 hepatitis B virus (HBV) or hepatitis C virus (HCV) infection

 -  Prior treatment with cluster of differentiation (CD)137 agonists or immune checkpoint
 blockade therapies, including anti Cytotoxic T Lymphocyte-Associated 4 (CTLA4),
 anti-programmed death 1 (PD-1), and anti-PD-L1 therapeutic antibodies

 -  Treatment with systemic immunostimulatory agents within 4 weeks or five half-lives of
 the drug, whichever is shorter, prior to initiation of study treatment

 -  Treatment with systemic immunosuppressive medication within 2 weeks prior to
 initiation of study

 -  History of seizure or any condition that may predispose to seizure within 12 months
 prior to study treatment, including history of unexplained loss of consciousness or
 transient ischemic attack