Abstract
184 Background: We previously found that men with AR-V7 (+) poor risk mCRPC have a low chance of benefit with abiraterone or enzalutamide. The benefits of subsequent taxane chemotherapy based on AR-V7 status may help inform treatment decisions. Methods: We conducted a multicenter prospective study of men with poor risk mCRPC (PROPHECY, NCT02269982) starting Abi or Enza and subsequent taxane chemotherapy. AR-V7 status from CTCs was assessed before abi/enza and again before taxane chemotherapy using the Epic nuclear protein assay or the Johns Hopkins Adnatest assay. The primary endpoint was to test the association of AR-V7 with radiographic/ clinical progression free survival (PFS) and OS with taxane chemotherapy, using the proportional hazards model, adjusting for Cell Search enumeration and clinical risk score. Results: We enrolled 118 men with mCRPC starting Abi/Enza; of these, 51 were evaluable with CTC AR-V7 testing and received subsequent taxane chemotherapy. With 50 PFS events, see table for final results. While AR-V7 positivity was associated with worse outcomes overall, AR-V7 (+) patients had similar PFS, OS, and confirmed >50% PSA declines adjusting for CTC enumeration and clinical prognostic factors. Concordance between the two AR-V7 assays pre-taxane was 0.78 (kappa 0.46). AR-V7 positivity increased at progression on abi/enza, but not following taxane chemotherapy. Conclusions: Men with AR-V7 positive mCRPC have poor outcomes, but may benefit from taxane chemotherapy after progression on abi/enza. AR-V7 may provide a helpful predictive biomarker to guide treatment with a second AR inhibitor or a taxane. Clinical trial information: NCT02269982. [Table: see text]
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