The objective of the project is to identify novel biomarkers for metastatic castration-resistant prostate cancer (mCRPC).Currently, radiographic imaging and serum prostate specific antigen (PSA) are the most common modalities used to track the course of mCRPC, but neither is believed to be an ideal surrogate for disease status. Preclinical data implicates signal transducer and activator of transcription 3 (STAT3) and prostate cancer stem cells (PCSCs) in prostate cancer pathogenesis.The project focuses on assessing these moieties in the peripheral blood of patients with mCRPC as an initial step towards Institutional Review Board (COH IRB 11004) approval to facilitate the proposed studies.