Despite the considerable treatment advances over the past 15 years, metastatic castration-resistant prostate cancer (mCRPC) continues to contribute to significant mortality and morbidity, with an estimated 34 130 deaths projected in the US in 2021.1 Because the molecular background of castration-resistant progression is incompletely understood, the selection of treatment for mCRPC is based on clinicopathologic risk stratification. However, individuals within clinically defined risk categories of mCRPC display widely different outcomes, with a subset of patients developing refractory disease associated with poor survival despite the many therapeutic options available.2 As such, the development and validation of prognostic and predictive biomarkers to improve the selection of therapy for mCRPC represent an important need.