Biomarker Study of in Men With PSA Progression on Abi for CR or CS PC (Bio-STAMP)

Inclusion Criteria: * Histological or cytological evidence of adenocarcinoma of the prostate * Undergone orchiectomy, or have been on luteinizing hormone-releasing hormone (LHRH) agonists or antagonists for at least 3 months prior to study enrollment. Patients on LHRH agonists/antagonists must remain on these agents for the duration of the study. * Currently receiving abiraterone (ZYTIGA or FDA approved generic) in the castration sensitive (CSPC) or castration resistant (CRPC) setting with PSA progression in the absence of visceral, bone or lymph node progression. PSA progression is defined as an increase in the PSA level of more than 50% above the nadir with two consecutive increases at least 2 weeks apart (based on Prostate Cancer Working Group Criteria, version 3 (PCWG3). * Minimum PSA must be ≥1.0 ng/dL. * Age 18 years of age or older. * ECOG performance status 0 or 1. * Have adequate organ function confirmed by the following laboratory values obtained within 14 days prior to enrollment: * absolute neutrophil count (ANC) ≥ 1.5 × 10\^9/L * platelets ≥ 100 × 10\^9/L * hemoglobin ≥ 10 g/dL, independent of transfusion ≤14 days of screening * aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 3 × upper limit of normal (ULN); if liver metastases, then ≤ 5 × ULN * total bilirubin ≤ 1.5 × ULN; \< 2 × ULN if hyperbilirubinemia is due to Gilbert's syndrome * serum albumin ≥ 30 g/L (3.0 g/dL) * Serum creatinine ≤ 1.5 x ULN; OR estimated glomerular filtration rate (GFR) ≥ 45 mL/min using the Cockcroft Gault formula * Participants with partners of childbearing potential must be willing to use at least two forms of effective birth control (one form must be a barrier method) during the dutasteride treatment period and for 6 months after last dose or 3 weeks after the last dose of abiraterone whichever is longer. Persons are considered to be of childbearing potential unless one or the following applies: * Is postmenopausal, defined as no menses for at least 12 months without an alternative medical cause * Considered permanently sterile. Permanent sterilization includes hysterectomy, bilateral salpingectomy, and/or bilateral oophorectomy. * Voluntary written consent prior to the performance of any research related activit Exclusion Criteria: * Previously demonstrated, clinically significant hypersensitivity (e.g., serious skin reactions, angioedema) to 5 alpha-reductase inhibitors (i.e. finasteride). * Prior use of Enzalutamide, Apalutamide, or Darolutamide for the treatment of prostate cancer.