Adding abiraterone for men with high-risk prostate cancer (PCa) starting long-term androgen deprivation therapy (ADT): Survival results from STAMPEDE (NCT00268476).

Abstract

LBA5003 Background: Abiraterone showed a survival advantage in men with castration-refractory prostate cancer. We assessed whether abiraterone would work earlier in the disease. STAMPEDE is a randomized controlled trial using a multi-arm multi-stage platform design. It recruits patients (pts) with high-risk locally advanced or metastatic PCa starting long-term ADT. We report the first comparative survival data. Methods: The standard-of-care (SOC) was ADT for 2+yrs; radiotherapy (RT) was mandated for men with N0M0 disease & encouraged for N+M0. Stratified randomization allocated pts 1:1 to SOC or SOC+abiraterone 1000mg + prednisolone 5mg daily. Treatment duration depended on stage & intent to give radical RT: pts not having RT or M1 disease, treatment continued until PSA, radiological & clinical progression; otherwise treatment continued until the earlier of 2 years or all types of progression. The primary outcome measure was death from any cause. Comparison to control for survival had 90% power at 2.5% 1-sided alpha for hazard ratio (HR) of 0.75, requiring ~267 control arm deaths, accounting for 3 intermediate lack-of-benefit analyses on failure-free survival (FFS). Analyses used Cox proportional hazards & flexible parametric models, adjusted for stratification factors. Results: 1,917 pts were contemporaneously randomized to these arms (Nov 2011- Jan 2014). Groups were balanced: median age 67yrs; 52% metastatic, 20% N+/X M0, 28% N0M0; 95% newly-diagnosed; median PSA 53ng/ml. Median follow-up was 40m. There were 262 control arm deaths (82% PCa). The adjusted HR = 0.63 (95% CI 0.52-0.76; p=0.115x10-7; 184 deaths) for SOC+Abi vs SOC, with 3yr OS improved from 76% to 83%. There were 535 control arm FFS events; the adjusted HR = 0.29 (95% CI 0.25-0.34; p = 0.377x10-63, 248 FFS events) for SOC+Abi vs SOC. Grade 3 & 4 adverse events were seen in 29% & 3% SOC, 41% & 5% SOC+Abi; Grade 5: 3 & 9 (1 & 2 related). Conclusions: The results show a clinically & statistically significant effect on overall survival & failure-free survival from adding abiraterone at start of ADT with a manageable increase in toxicity. ADT (+/- RT) + abiraterone is a new standard of care for this group. Clinical trial information: NCT00268476.