Predictive value of low testosterone concentrations during and prior to enzalutamide treatment in metastatic castration-resistant prostate cancer

•In CRPC, testosterone levels predict poor PSA response to enzalutamide treatment.•Low during treatment testosterone levels were associated with shorter PFS.•Low pretreatment testosterone levels were associated with shorter PFS.•FFS was also associated with testosterone levels in this patient cohort. Enzalutamide is an effective treatment for metastatic castration-resistant prostate cancer (mCRPC) patients. However, variances in responses are observed and there is a need for biomarkers predicting treatment outcome and selection. In this study, we aimed to explore the predictive value of testosterone for first-line enzalutamide treatment of mCRPC. A retrospective analysis of 72 mCRPC patients with no prior abiraterone or docetaxel treatment was performed. Serum testosterone was measured using a liquid chromatography tandem-mass spectrometry method. Association of pre- and during-enzalutimide treatment testosterone levels with progression-free survival (PFS) and failure-free survival (FFS) was investigated using univariate and multivariate Cox models. Testosterone levels were dichotomized into a low (Q1) and high (interquartile range-Q4) group. Median PFS (7.4 v. 20.8 months, P