Background: Men with M0 CRPC and rapidly rising prostate-specific antigen (PSA) are at high risk of developing metastatic (M1) CRPC. ENZA improves overall survival (OS) and radiographic progression-free survival in men with M1 CRPC. We hypothesized that ENZA will improve metastasis-free survival (MFS) in men with M0 CRPC. Methods: Eligible men with M0 CRPC, PSA doubling time ≤ 10 mo and PSA ≥ 2 ng/mL at screening continued androgen deprivation therapy (ADT) and were randomized 2:1 to ENZA 160 mg or PBO. The primary endpoint was MFS. Secondary endpoints included time to PSA progression, time to first use of new antineoplastic therapy, OS and safety. Results: In 1401 men, ENZA significantly prolonged median MFS (36.6 mo vs 14.7 mo [P< .0001]), time to first use of new antineoplastic therapy (39.6 mo vs 17.7 mo [P< .0001]) and time to PSA progression (37.2 mo vs 3.9 mo [P< .0001]) compared to PBO (Table). In the first interim analysis of OS there was a trend in favor of ENZA (hazard ratio [HR] = 0.80; P = .1519). Median duration of treatment was 18.4 mo vs 11.1 mo for ENZA vs PBO. Adverse events (AEs) were higher with ENZA vs PBO (any grade: 87% vs 77%; grade ≥ 3: 31% vs 23%; serious: 24% vs 18%); 10% with ENZA discontinued treatment due to AE vs 8% with PBO. Conclusions: In men with M0 CRPC and rapidly rising PSA, ENZA treatment resulted in a clinically meaningful and statistically significant 71% reduction in the risk of developing M1 CRPC. AEs were consistent with the established safety profile of ENZA. Clinical trial information: NCT02003924

^aFinal analysis; ^binterim analysis CI, confidence interval; NR, not reached