A Study of Abiraterone Acetate Plus Prednisone With or Without Abemaciclib (LY2835219) in Participants With Prostate Cancer

Inclusion Criteria:

• Histologically confirmed adenocarcinoma of the prostate.

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

• Progressive disease at study entry demonstrated during continuousandrogen-deprivation therapy (ADT)/post orchiectomy defined as one or more of thefollowing:

• 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 & 6inhibitors.

• Prior cytotoxic chemotherapy for metastatic castration resistant prostate cancer (participants treated with docetaxel in the metastatic hormone-sensitive prostatecancer [mHSPC] are eligible). Prior radiopharmaceuticals for prostate cancer, orprior enzalutamide, apalutamide, darolutamide or sipuleucel-T. Participants who hadprior 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 largepills.

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