TPS5094Background: Treatment for nonmetastatic castration-resistant prostate cancer (nmCRPC) other than continuing androgen deprivation therapy (ADT) remains an unmet need. There are no approved therapies for preventing metastatic disease in nmCRPC. Pts with nmCRPC who have shorter prostate-specific antigen doubling time (PSADT) are at higher risk for metastatic disease or death. ODM-201, a novel second-generation oral androgen receptor inhibitor, has demonstrated a tolerable safety profile and antineoplastic activity in progressive CRPC. The ARAMIS trial will evaluate the efficacy and safety of ODM-201 in high-risk nmCRPC pts. Methods: This randomized, double-blind, placebo-controlled phase 3 trial (NCT02200614) involves > 450 sites in > 33 countries. 1500 pts on ADT will be randomized 2:1 to ODM-201 600 mg or placebo BID. Pts will be stratified by PSADT and baseline bone-targeting agent use. Eligibility criteria include nmCRPC, PSADT ≤ 10 months, and screening PSA ≥ 2 ng/mL. 90% power to detect a target...