1 Division of Oncology, Department of Medicine, University of Washington/Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA. schweize@uw.edu eantona1@jhmi.edu.
2 Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA. schweize@uw.edu eantona1@jhmi.edu.
Analysis of tumor-derived cell-free DNA in blood yields insights into drug resistance in patients with castration-resistant prostate cancer (Romanel et al., this issue).