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