The Prophecy Trial: Multicenter Prospective Trial Of Circulating Tumor Cell (Ctc) Ar-V7 Detection In Men With Mcrpc Receiving Abiraterone (A) Or Enzalutamide (E).

5004Background: It is unclear if CTC AR-V7 detection is a valid predictive biomarker of clinical efficacy in men with mCRPC receiving A/E or just an indicator of aggressive disease and high tumor burden. Methods: We conducted a multicenter prospective study of circulating biomarkers in men with high-risk mCRPC (PROPHECY, NCT02269982) starting A/E. The primary endpoint was association of baseline AR-V7 with radiographic/clinical progression free survival (PFS), using the Johns Hopkins modified-AdnaTest CTC AR-V7 mRNA assay and the Epic Sciences CTC nuclear AR-V7 protein assay. Overall survival (OS) and PSA decline were key secondary endpoints. Results: We enrolled 118 men with mCRPC starting A/E; 52% had ≥5 Cellsearch CTCs, 36% had prior A/E. On study therapy was A (n = 56), E (n = 59) or both A/E (n = 3). AR-V7 detection by the JHU AR-V7 assay and the Epic AR-V7 assay were independently associated with worse PFS and OS after adjusting for CTC count and established clinical factors (see below table). Conco...