AR and neoplasm: Focal copy number alterations were also frequent, including PTEN deletion (20 of 59 (28.8%) high tumor content cfDNA samples, 11 (65%) of which are focal deep deletions (Supplementary Figure 10)), and focal AR amplification (36 of 93 (39%) cfDNA samples, including 32 of 59 (54%) high tumor content mCRPC samples) (Supplementary Figure 10, Supplementary Table 1), both of which are biomarkers of poor prognosis and/or resistance to second-line anti-androgens (abiraterone and enzalutamide), particularly when observed in cfDNA [23, 52, 53, 60] (see Supplementary Results).