P1/2 | "Early MR (by C2D1) was achieved in 35% of patients and strongly associated with improved rPFS and OS while PSA50 responses by C2D1 were not observed in any patients. The rPFS benefit of adding olaparib to radium-223 appeared more evident in those who achieved a MR. Early on treatment ctDNA dynamics in bone-dominant mCRPC may be a valuable tool for treatment decisions with radium-223 therapy."