Androgen receptor splice variant, AR-V7, and resistance to enzalutamide and abiraterone in men with metastatic castration-resistant prostate cancer (mCRPC).

Genitourinary (Prostate) Cancer
Session Type and Session Title: 
Oral Abstract Session, Genitourinary (Prostate) Cancer
Abstract Number: 
J Clin Oncol 32:5s, 2014 (suppl; abstr 5001)
Emmanuel S. Antonarakis, Changxue Lu, Hao Wang, Brandon Luber, Mary Nakazawa, Yan Chen, Jeffrey C. Roeser, Helen L. Fedor, Tamara L. Lotan, Qizhi Zheng, Angelo M. De Marzo, John T. Isaacs, William B. Isaacs, Rosa Nadal, Channing Judith Paller, Samuel R. Denmeade, Michael Anthony Carducci, Mario A. Eisenberger, Jun Luo; The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD; The Brady Urological Institute, The Johns Hopkins Hospital, Baltimore, MD; Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, MD

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Abstract Disclosures


Background: Androgen receptor splice variant-7 (AR-V7) is a truncated form of the androgen receptor that lacks the ligand-binding domain, the target of enzalutamide and abiraterone, but remains constitutively active as a transcription factor. We hypothesized that detection of AR-V7 in circulating tumor cells (CTCs) from men with mCRPC may be associated with primary resistance to enzalutamide and abiraterone. Methods: We used quantitative reverse-transcription PCR (qRT-PCR) to interrogate CTCs for the presence or absence of AR-V7 from prospectively enrolled patients with mCRPC initiating treatment with enzalutamide or abiraterone. We examined associations between AR-V7 status and PSA response rates, PSA progression-free survival (PSA-PFS), and clinical/radiographic progression-free survival (PFS). Multivariable Cox regression analyses were performed to determine the independent effect of AR-V7 status on these clinical outcomes. 30 men (per cohort) were required to detect a difference in PSA response rates from 10% (in AR-V7–positive men) to 60% (in AR-V7–negative men), using a 2-sided α=0.10 and β=0.15. Results: 31 enzalutamide-treated patients and 31 abiraterone-treated patients were enrolled, of which 38.7% and 19.4% had detectable AR-V7 from CTCs, respectively. Among men receiving enzalutamide, AR-V7–positive patients had inferior PSA response rates (0% vs 52.6%, P=0.004), PSA-PFS (median 1.4 vs 5.9 months, P<0.001), and PFS (median 2.1 vs 6.1 months, P<0.001) compared to AR-V7–negative patients. Similarly, among men receiving abiraterone, AR-V7–positive patients had inferior PSA response rates (0% vs 68.0%, P=0.004), PSA-PFS (median 1.3 months vs not reached, P<0.001), and PFS (median 2.3 months vs not reached, P<0.001). The negative prognostic impact of AR-V7 was maintained after adjusting for full-length AR expression levels. Conclusions: Detection of AR-V7 in CTCs from men with mCRPC is associated with resistance to enzalutamide and abiraterone. AR-V7 status may be used as a biomarker to predict resistance to AR-targeting agents, facilitate treatment selection, and fuel the development AR N-terminal domain inhibitors.