Jayaram et al[1] describe the utility of evaluating plasma I AR i copy number (CN) to identify patients with aggressive prostate cancer who respond poorly to androgen receptor (AR) targeting therapy and have an overall poor prognosis. 4 Reyes EE, VanderWeele DJ, Isikbay M, et al: Quantitative characterization of androgen receptor protein expression and cellular localization in circulating tumor cells from patients with metastatic castration-resistant prostate cancer. 6 Conteduca V, Wetterskog D, Sharabiani MTA, et al: Androgen receptor gene status in plasma DNA associates with worse outcome on enzalutamide or abiraterone for castration-resistant prostate cancer: A multi-institution correlative biomarker study. [Extracted from the article]