Subjects with mCRPC who were receiving standard-of-care therapy or treatment in a clinical trial [including trials combining AR therapies with other agents, a trial of the PARP inhibitor olaparib (37 (link)), and a trial of the Aurora kinase A inhibitor alisertib in patients with neuroendocrine features (14 (link))] and who had disease amenable to biopsy under radiographic guidance were considered for inclusion at one of seven SU2C-PCF (Stand Up to Cancer/Prostate Cancer Foundation) International Prostate Cancer Dream Team consortium sites (Dana-Farber Cancer Institute, Karmanos Cancer Institute, Memorial Sloan Kettering Cancer Center, Royal Marsden, University of Michigan, University of Washington, and Weill Cornell Medicine) (5 (link)). All subjects included in this study provided written consent for research use of tumor tissue with institutional review board approvals or appropriate waivers (Office of Human Research Studies at the Dana-Farber Cancer Institute, Wayne State University Institutional Review Board, Memorial Sloan Kettering Cancer Center Institutional Review Board/Privacy Board, Royal Marsden Ethics Committee, University of Michigan Medical School Institutional Review Board, University of Washington Institutional Review Board, and Weill Cornell Medicine Institutional Review Board). Clinical data, including treatment history, duration of therapy, and survival, were collected using a web-based electronic data capture. All samples and clinical data were deidentified.