Inclusion Criteria:

          -  Histologically confirmed adenocarcinoma of the prostate.

          -  Metastatic prostate cancer documented by positive bone scan and/or measurable soft
             tissue metastatic lesions by CT or magnetic resonance imaging (MRI).

          -  Progressive disease at study entry demonstrated during continuous androgen-deprivation
             therapy (ADT)/post orchiectomy defined as one or more of the following:

               -  PSA progression

               -  Radiographic progression per Response Evaluation Criteria in Solid Tumors
                  (RECIST)1.1 for soft tissue and/or per Prostate Cancer Working Group 3 (PCWG3)
                  for bone, with or without PSA progression

          -  Have adequate organ function.

          -  Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-1.

        Exclusion Criteria:

          -  Prior therapy with cytochrome P450 (CYP)17 inhibitors.

          -  Prior treatment with abemaciclib or any cyclin-dependent kinase (CDK) 4 & 6
             inhibitors.

          -  Prior cytotoxic chemotherapy for metastatic castration resistant prostate cancer
             (participants treated with docetaxel in the metastatic hormone-sensitive prostate
             cancer [mHSPC] are eligible). Prior radiopharmaceuticals for prostate cancer, or prior
             enzalutamide, apalutamide, darolutamide or sipuleucel-T. Participants who had prior
             radiation or surgery to all target lesions.

          -  Currently enrolled in a clinical study involving an investigational product.

          -  Gastrointestinal disorder affecting the absorption or ability to swallow large pills.

          -  Clinically significant heart disease, active or chronic liver disease, moderate/severe
             hepatic impairment (Child-Pugh Class B and C).