A Study of Abemaciclib (LY2835219) With Abiraterone in Men With Prostate Cancer That Has Spread to Other Parts of the Body and is Expected to Respond to Hormonal Treatment (Metastatic Hormone-Sensitive Prostate Cancer)

Radiographic Progression-Free Survival (rPFS) Assessed by Investigator

Timeframe: From Date of Randomization to Radiographic Disease Progression or Death from Any Cause (up to 22 months)

The rPFS time is measured from the date of randomization to the earliest date of investigator determined radiographic disease progression (by objective radiographic disease assessment per response evaluation criteria in solid tumors (RECIST) version 1.1 for soft tissue AND/OR radionuclide bone scan using prostate cancer working group 3 -PCWG3 criteria for bone) or death from any cause, whichever occurs first.

Radiographic Progression-Free Survival (rPFS) Assessed by Blinded Independent Central Review (BICR)

Timeframe: From Date of Randomization to Radiographic Disease Progression or Death from Any Cause (up to 22 months)

The rPFS time is measured from the date of randomization to the earliest date of investigator determined radiographic disease progression (by objective radiographic disease assessment per response evaluation criteria in solid tumors (RECIST) version 1.1 for soft tissue AND/OR radionuclide bone scan using prostate cancer working group 3 -PCWG3 criteria for bone) or death from any cause, whichever occurs first.

Castration-resistant Prostate Cancer (CRPC)-Free Survival

Timeframe: Randomization to the earliest date of PSA or radiographic progression with a testosterone level of ≤50 ng/dL; or death from any cause (up to 22 months)

CRPC-free survival is defined as the time from the date of randomization to the earliest date of castration resistance, as demonstrated by any of the following (whichever occurs earliest): Confirmed prostate-specific antigen (PSA) progression with serum testosterone ≤50 nanogram/deciliter (ng/dL) (≤1.73 nanomoles per liter(nmol/L)). Investigator-assessed radiographic progression with serum testosterone ≤50 ng/dL (≤1.73 nmol/L). Death from any cause.

Overall Survival (OS)

Timeframe: From Date of Randomization to Date of Death Due to Any Cause (Up to 22 Months)

The OS time is measured from the date of randomization to the date of death from any cause. If the participant was alive or lost to follow-up at the time of data analysis, OS data were censored on the last date the participant was known to be alive.

Time to Pain Progression

Timeframe: Randomization to pain progression (up to 22 months)

Time to Deterioration in Health-Related Quality of Life (HRQoL) Measured by Functional Assessment of Cancer Therapy-Prostate (FACT-P) - Physical Well-Being Subscale

Timeframe: Randomization to the date of the first clinically meaningful HRQoL deterioration (up to 22 months)

Time to deterioration in health-related quality of life (HRQoL) was defined as the time from randomization to the date of the first clinically meaningful HRQoL deterioration on 2 consecutive measurements. HRQoL evaluation was performed using the FACT-P questionnaire. Physical Well-Being subscale is a subsection of FACT-P questionnaire. FACT-P consists of 39 core items to assess health related quality of life in participants with prostate cancer. It consisted of 5 sub-scales assessing physical well-being (7 items), social/family well-being (7 items), emotional well-being (6 items), functional well-being (7 items), and prostate cancer subscale (12 items). Each item is rated from 0 (Not at all) to 4 (Very much) and combined to produce subscale scores. FACT-P total score was the sum of all 5 subscale scores. It ranged from 0 to 156 with higher score indicating better quality of life. Physical well-being subscale score ranges from 0 to 28 with high score indicating better quality of life.

Time to Deterioration in Health-Related Quality of Life (HRQoL) Measured by Functional Assessment of Cancer Therapy-Prostate (FACT-P) - Prostate Cancer Subscale

Timeframe: Randomization to the date of the first clinically meaningful HRQoL deterioration (up to 22 months)

Time to deterioration in health-related quality of life (HRQoL) was defined as the time from randomization to the date of the first clinically meaningful HRQoL deterioration on 2 consecutive measurements. HRQoL evaluation was performed using the FACT-P questionnaire. Prostate Cancer Subscale is a subsection of FACT-P questionnaire. FACT-P consists of 39 core items to assess health related quality of life in participants with prostate cancer. It consisted of 5 sub-scales assessing physical well-being (7 items), social/family well-being (7 items), emotional well-being (6 items), functional well-being (7 items), and prostate cancer subscale (12 items). Each item is rated from 0 (Not at all) to 4 (Very much) and combined to produce subscale scores. FACT-P total score was the sum of all 5 subscale scores. It ranged from 0 to 156 with higher score indicating better quality of life. Prostate cancer subscale score ranges from 0 to 48 with high score indicating better quality of life.

Pharmacokinetics (PK): Maximum Plasma Concentration at Steady State (Cmax,ss) of Abemaciclib

Timeframe: Predose on Cycle 1 Day 1, Predose and Predose on Cycle 2 Day 1 and Predose on Cycle 3 Day 1 (28 Day Cycles)

Maximum plasma concentration at steady state (Cmax,ss) of abemaciclib was evaluated.