Sequential therapy of abiraterone and enzalutamide in castration-resistant prostate cancer: a systematic review and meta-analysis

Background: This systematic review and meta-analysis aimed to assess the prognostic value of sequential of abiraterone (ABI) and enzalutamide (ENZ) therapy in patients with castration-resistant prostate cancer (CRPC). Methods: PUBMED, Web of Science, Cochrane Library, and Scopus databases were searched for articles published prior to December 2019 according to the Preferred Reporting Items for Systematic Review and Meta-analysis statement. Studies were deemed eligible if they compared overall survival (OS), combined progression-free survival (PFS), combined prostate specific antigen (PSA)-PFS, and PSA response rates in CRPC patients receiving sequential ABI/ENZ or vice versa. PSA response to both the first and second agents was defined as a >50% decrease in PSA achieved with each of these agents. Formal meta-analyses were performed for these outcomes. Results: Ten studies with 1096 patients were eligible for the systematic review and eight studies with 643 patients for the meta-analysis. The ABI-to-ENZ sequence was significantly associated with better PFS (pooled hazard ratio (HR): 0.62, 95% confidential interval (CI): 0.49–0.78, P < 0.001), and PSA–PFS (pooled HR: 0.48, 95% CI: 0.38–0.61, P < 0.001) than the ENZ-to-ABI sequence. PSA response rates of both agents were significantly better with the ABI-to-ENZ sequence (risk ratio: 0.21, 95% CI: 0.09–0.47, P < 0.001). In contrast, treatment sequence was not significantly associated with OS (pooled HR: 0.77, 95% CI: 0.59–1.01, P = 0.055). Conclusions: ABI-to-ENZ sequential therapy in patients with CRPC was associated with better PFS, PSA–PFS, and PSA response rates. Regardless of sequencing, response to drug therapy was transient for both ABI and ENZ when either agent was used as a secondary therapy. Despite this, treatment sequencing is important to achieve the maximum possible benefit from available drugs in CRPC.