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

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
( 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