A Study to Learn About the Study Medicines Called Enzalutamide and Abiraterone in People With Metastatic Castration-resistant Prostate Cancer

The purpose of this real-world study is to learn about the effects of 2 study medicines called enzalutamide and abiraterone used to treat metastatic castration-resistant prostate cancer (mCRPC). Prostate cancer is one of the most common cancers in men. The prostate is a gland in the male body that helps make semen. Most prostate cancers need male sex hormones, such as testosterone, to grow. Prostate cancer that keeps growing even when the amount of testosterone in the body is reduced to very low levels is known as "castration-resistant". Metastatic cancer is a cancer that has spread to other parts of the body. This is a real-world study, not a clinical trial. This means that researchers will look at what happens when men receive the treatments prescribed by their own doctor as part of their usual healthcare treatment. In this study, researchers will use information from the Flatiron Electronic Health Record (EHR) database. The study will include patients' information from the database for men who: * Were confirmed by medical tests to have mCRPC * Started first-line treatment with enzalutamide or abiraterone (index date) for mCRPC * Had not received chemotherapy treatment before index date * Were 18 years of age or older on index date Men who are part of this study will receive enzalutamide or abiraterone as part of their usual treatment for mCRPC. We will compare the following between men receiving enzalutamide and men receiving abiraterone: * time from treatment start until death, * treatment duration, and * time to next treatment. This study will use patient information from the database until the end of information that is available.