AR and neoplasm: These results are consistent with those seen when restricting analyses to samples from patients on or starting therapy separately (Supplementary Figure 16), and together confirm previous reports that cfDNA detectable AR amplification predicts resistance to abiraterone or enzalutamide [23, 52, 53], while supporting AR amplification (and high tumor content) as a more general poor prognostic factor, similar to circulating tumor cell (CTC) count [65, 66].