Focal RB1 deletion, a frequent alteration in neuroendocrine/small-cell prostatic carcinoma [45, 61], was also detectable by our approach, with 4 samples (4.3%) (4 patients) exhibiting focal deep deletions (Supplementary Figure 10), including 1 from a patient (TP1320) with detectable AR amplification, who (post-ADT and a single course of docetaxel) progressed rapidly on abiraterone over the course of 3 months on therapy with PCa-related death 4 months after cfDNA profiling (Supplementary Table 2; see Supplementary Results). Here, RB1 is linked to prostate small cell carcinoma.