This was an IRB-approved retrospective study. Eligibility: confirmed diagnosis of mCRPC, first-line treatment with an ARAT (abiraterone or enzalutamide)....Median PFS and OS for AR wt was significantly higher than AR+ pts. In the subgroup analyses median PFS and OS were similar regardless of AR amp or AR mut....In this hypothesis-generating study, pts with mCRPC harboring AR alterations in ctDNA had worse outcomes on first-line ARAT compared to AR wt.