Immediate Prostate-specific Antigen Decline After Enzalutamide Following Abiraterone Predicts Survival in Castration-resistant Disease.

Abstract

Although the sequential use of abiraterone and enzalutamide is not recommended because of possible cross-resistance, many patients with metastatic castration-resistant prostate cancer (mCRPC) are receiving sequential abiraterone and enzalutamide in the real world, and a subset of patients can benefit from sequential therapy with these drugs. This study aimed to identify patients who could benefit from the sequential use of enzalutamide after abiraterone use. We included 70 patients with mCRPC who received enzalutamide sequentially following abiraterone treatment. Decline in the prostatespecific antigen (PSA) levels at 4 weeks after enzalutamide initiation and the association between decline in PSA levels and survival were analyzed. Sixteen men (22.9%) achieved a decline of >50% in PSA levels after 4 weeks of enzalutamide administration. Overall survival (OS) after enzalutamide among men with >50% decline at 4 weeks was significantly better than that among men with a PSA decline <50% (not reached vs. 34 months, p=0.008). OS after first-line abiraterone treatment for men with PSA decline >50% and <50% was not reached and 46 months, respectively (p=0.007). A PSA decline of >50% at 4 weeks of enzalutamide administration was an independent predictor of longer OS. A PSA decline of >50% at 4 weeks after the start of sequential enzalutamide treatment following abiraterone treatment predicted long-term survival in patients with mCRPC. Early PSA decline can identify patients who benefit from second-line enzalutamide after abiraterone treatment and can be useful as a decision-making tool regarding treatment.