Miyazawa Y, et al. - A total of 241 subjects with metastatic castration-resistant prostate cancer (mCRPC) who were treated with enzalutamide (ENZ) were assessed by the experts in order to evaluate the early prostate-specific antigen (PSA) response to ENZ by measuring the PSA doubling time (PSADT) and PSA velocity (PSAV) while observing oncologic outcomes and survival in Japanese subjects. Seventy-seven good response cases, 125 acquired resistance cases, and 39 primary resistance cases were noted. Predocetaxel, PSA-progression-free survival and overall survival (OS) were significantly greater vs post docetaxel. Multivariate analysis of prognostic factors, including PSA response at 4 weeks, was done via Cox regression analysis. Important predictors of OS were ECOG PS, hemoglobin, time to CRPC, docetaxel treatment history, and a PSA decline of 50% at 4 weeks. PSA kinetic factors, such as PSADT and PSAV, Hb, time to CRPC, PSADT, and PSAV, were all shown in the multivariate analysis as predictive of OS following PSA-progression, in cases of AR (n=125). Hence, for mCRPC subjects, PSA dynamics following ENZ administration may be a beneficial prognostic factor.