Abstract
303 Background: Abiraterone acetate (a prodrug of abiraterone, which is a selective inhibitor of androgen biosynthesis) combined with prednisone/prednisolone (AA+P) and enzalutamide (ENZ) (an androgen-receptor–signalling inhibitor) have proven survival benefit in men with metastatic castration resistant prostate cancer (mCRPC) in chemo naïve and prior chemo patients. There have been no studies directly comparing the effectiveness of ENZ to AA+P in mCRPC patients. Methods: A retrospective, survival analysis study of 143 real world mCRPC patients (90 in AA+P and 53 in ENZ group) was conducted. Patients who started their treatment between 1st February 2012 and 31st May 2016 were included. The primary endpoint was biochemical progression free survival (PFS). Secondary end points were radiographic progression free survival (rPFS) and overall survival (OS). Data was analysed using Cox proportional hazards models, adjusting for covariates: prior radical or palliative treatment; Gleason score; baseline PSA; age; and chemo naïve or not. Results: After median follow up of 15 months (IQR 7 to 23) 112 events of biochemical progression were observed (71 in AA+P and 41 in ENZ). 41%in AA+P group and 30% patients in ENZ group received prior chemo. The chance of biochemical progression was significantly lower among ENZ patients than AA+P patients, when adjusting for all covariates in the Cox PH model (Hazard Ratio 0.54, 95% CI 0.35 to 0.82, p=0.004. There was a trend implying the chance of rPFS could be higher among ENZ patients than AA+P patients (HR 1.24, 95% CI 0.76 to 2.02, p=0.4). OS is lower among ENZ patients than AA+P patients, when adjusting for all covariates in the Cox PH model (HR 0.91, 95% CI 0.59 to 1.41, p=0.7). 38% of ENZ patients reported fatigue compared to 16% of AA+P patients while hypertension was reported slightly more in AA+P patients than in ENZ patients. Conclusions: This study showed a statistically significant difference in biochemical progression-free survival, favouring ENZ, but no significant difference in radiographic progression-free survival or overall survival.
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