AMG 386 and Abiraterone for Advanced Prostate Cancer

Background: * Advanced prostate cancer is treated with surgery or drugs that lower the levels of androgens (male hormones) in the body. However, some cancers become resistant to this treatment. These types of cancers are known as castration-resistant prostate cancers. * Interfering with the growth of blood vessels that feed tumors can slow prostate cancer growth. Trebananib (AMG 386), a new anticancer drug, targets the blood vessels that feed tumors. It has been tested for different types of cancer, but not for prostate cancer. Researchers want to see if AMG 386 can slow disease progression in men with castration-resistant prostate cancer. AMG 386 will be given with abiraterone and prednisone, two drugs that are also used to treat advanced prostate cancer. Objectives: \- To test the safety and effectiveness of AMG 386 with abiraterone for castration-resistant prostate cancer. Eligibility: \- Men at least 18 years of age with castration-resistant prostate cancer. Design: * Participants will be screened with a physical exam, medical history, and imaging studies. Blood and urine samples will also be collected. * Participants will be separated into two groups. * The first group will have AMG 386 once per week for a total of four doses during a 28-day cycle. They will also take abiraterone once a day and prednisone twice a day, every day of the cycle. * The second group will not have AMG 386. They will take abiraterone once a day and prednisone twice a day, every day of the 28-day cycle. * Treatment will be monitored with frequent blood tests and imaging studies. * Participants will continue to take the study drugs as long as the disease does not progress and there are no severe side effects.