Differential side effects profile in patients with mCRPC treated with abiraterone or enzalutamide: a meta-analysis of randomized controlled trials

Background Abiraterone and enzalutamide are currently approved for mCRPC patients. Both drugs have distinct mechanisms of action and may have different toxicity profile. There are limited data comparing the side effects of abiraterone and enzalutamide. We performed a meta-analysis of randomized controlled trials (RCT) to better characterize the risk of adverse events associated with both drugs. Methods We performed a literature search on MEDLINE for studies reporting abiraterone and enzalutamide side effects from January 1966 to July 31, 2015. Abstracts presented at ASCO meetings from 2004 to 2015 were selected manually. Phase III RCT were included in analysis. We assessed the risk of adverse events reported in RCT by performing two meta-analyses: abiraterone-prednisone vs. placebo-prednisone (2,283 pts) and enzalutamide vs. placebo (2,914 pts). Summary of incidence, relative-risks (RR), and 95% confidence intervals (CI) were calculated using random-effects or fixed-effects models based on the heterogeneity of included studies. Results Overall, enzalutamide was not associated with all-grade (RR 1.06 - 95% CI 0.67-1.65) or grade ≥3 (RR 0.81 - 95% CI 0.28-2.33) cardiovascular events, but was associated with increased risk of all-grade fatigue (RR 1.29 - 95% CI 1.15-1.44). On the other hand, abiraterone was associated with increased risk of all-grade (RR 1.28 - 95% CI 1.06-1.55) and grade ≥3 (RR 1.76 - 95% CI 1.12-2.75) cardiovascular events, but was not associated with all-grade (RR 0.85 - 95% CI 0.58-1.23) or grade ≥3 (RR 1.07 - 95% CI 0.97-1.19) fatigue. Conclusions In this meta-analysis, abiraterone was associated with an increased risk of cardiovascular events, while enzalutamide was associated with an increased risk of fatigue.