AR-V7 and AR-FL expression is associated with clinical outcome: a translational study in patients with castrate resistant prostate cancer

OBJECTIVES: To investigate if full-length androgen receptor (AR-FL) is associated with resistance to AR-directed therapy independently and/or combined with AR splice variant 7 (AR-V7). PATIENTS AND METHODS: Plasma samples were prospectively collected from 73 patients with CRPC before first or second-line AR-directed therapy. mRNA was isolated from exosomes and AR-FL and AR-V7 were analyzed by ddPCR. RESULTS: AR-FL was detected in all patients while 22% were AR-V7+ at baseline. AR-FL expression was significantly higher in AR-V7+ vs AR-V7- patients (p<0.0001). Stratifying patients by tertiles for AR-FL expression, PFS was 22 vs 18 vs 4 months for lower vs intermediate vs higher tertile, respectively (p=0.0003). Median PFS and OS were significantly longer in AR-V7- vs AR-V7+ patients (20 vs 4 months, p<0.0001; not reached vs 9 months, p<0.0001, respectively). CONCLUSIONS: Resistance to AR-directed therapy is associated with the presence of AR-V7; however, AR-FL expression may help better refine response and survival of patients to AR-directed therapy. Both biomarkers, if validated in prospective trials, may be used to select the best treatment strategy.