Safety and Tolerability of Atezolizumab (ATZ) in Combination With Radium-223 Dichloride (R-223-D) in Metastatic Castrate-Resistant Prostate Cancer (CRPC) Progressed Following Treatment With an Androgen Pathway Inhibitor

Inclusion Criteria:

Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
Life expectancy greater than or equal to (>/=) 12 weeks
Histologically confirmed, castrate-resistant adenocarcinoma of the prostate
Measurable disease according to RECIST v1.1
Multiple bone metastases within 12 weeks prior to study drug
Participants receiving bisphosphonate or denosumab therapy must have been on a stable dose for at least 4 weeks
Visceral metastasis and/or lymphadenopathy
Tumors that are amenable to serial biopsy
Disease progression according to Prostate Cancer Working Group 2 (PCWG2) criteria during or following treatment with at least one second generation androgen pathway inhibitor (for example, enzalutamide, abiraterone) for metastatic prostate cancer
Adequate hematologic and end-organ function
One prior taxane-containing regimen for mCRPC, or refusal or ineligibility of a taxane-containing regimen

Exclusion Criteria:

History of small-cell or neuroendocrine prostate carcinoma
Treatment with approved anti-cancer therapy (with the exception of abiraterone) within 3 weeks of study drug. Abiraterone must not be administered within 2 weeks prior to initiation of study treatment
Participation in another clinical trial/investigation within 28 days prior to study drug
Brain metastases or active leptomeningeal disease (with the exception of participants with treated epidural disease and no other epidural progression)
Uncontrolled tumor-related pain
Uncontrolled hypercalcemia
Significant cardiovascular disease
History of autoimmune disease except controlled/treated hypothyroidism, type 1 diabetes mellitus, or certain skin disorders
Prior allogeneic stem cell or solid organ transplant
History of pulmonary fibrosis/inflammation, including active tuberculosis
Human immunodeficiency virus (HIV) or hepatitis B or C
Prior treatment with cluster of differentiation (CD) 137 agonist, anti-programmed death (PD) 1, or anti-programmed death ligand (PD-L) 1 therapeutic antibody or pathway-targeting agents
Immunostimulants within 4 weeks or immunosuppressants within 14 days prior to study drug
Prior radium-223 dichloride or hemibody external radiotherapy
Systemic strontium-89, samarium-153, rhenium-186, or rhenium-188 for bone metastases within 24 weeks prior to initiation of study treatment
Spinal compression or structurally unstable bone lesions suggesting impending pathologic fractures based on clinical findings and/or magnetic resonance imaging (MRI)
Bone marrow dysplasia
Unmanageable fecal incontinence