INTRODUCTION - Metastatic prostate cancer is an incurable disease that is treated with a variety of hormonal therapies targeting various nodes of the androgen receptor (AR) pathway. Invariably patients develop resistance and become castration resistant. Common treatments for castration-resistant disease include novel hormonal therapies, such as abiraterone and enzalutamide, chemotherapy, immunotherapy and radiopharmaceuticals. As this disease generally remains incurable, understanding the molecular underpinnings of resistance pathways is critical in designing therapeutic strategies to delay or overcome such resistance.