Almassi N, et al. - The objective of this study is to figure out if the HSD3B1 (1245C) genotype is predictive of clinical response to extragonadal androgen ablation with nonsteroidal 17α-hydroxylase/17,20-lyase (CYP17A1) inhibition in men with metastatic castration-resistant prostate cancer (CRPC). Inheritance of the HSD3B1 (1245C) variant allele, which is a predictive biomarker of resistance to castration, is also a predictive biomarker of sensitivity to extragonadal androgen ablation with a nonsteroidal CYP17A1 inhibitor. For patients with prostate cancer, these outcomes signal a possible pathway of treatment stratification.