BACKGROUND:Major advances in our understanding of the underlying biology of prostate cancer have helped to herald a new era in the treatment of castration-resistant prostate cancer (CRPC), with 5 new agents having shown a survival advantage in the last 3 years and an impressive number of promising novel agents now entering the clinic. CONTENT:We discuss the challenges facing drug development for CRPC and strategies to meet these challenges, with a focus not only on the development of predictive and intermediate endpoint biomarkers, but also on novel hypothesis-testing, biomarker-driven clinical trial designs. SUMMARY:With several promising agents now entering the clinic, there is increasing pressure to rethink drug development for CRPC to ensure that novel agents are appropriately evaluated and that patients and resources are appropriately allocated. We envision that biomarker-driven, reiterative clinical trials will have a major impact on CRPC treatment through the testing of robust scientific hypotheses with rationally designed drugs and drug combinations administered to selected patients.