Klin Onkol 2018; 31(1): 9-14. DOI: 10.14735/amko20189.
Background: Several systemic treatment options are currently available for patients with metastatic castration-refractory prostate cancer (mCRPC), including the androgen-receptor targeting agents (ARTA) enzalutamide and abiraterone, the taxanes docetaxel and cabazitaxel, and the radioisotope drug 223-radium dichloride. In some patients with mCRCP, alternative splicing of androgen receptor (AR) mRNA occurs, resulting in the formation of a truncated AR lacking the androgen-binding domain. These receptors activate downstream signalling pathways even without the ligand. Recent studies show that the presence of the AR-V7 (ARV – AR variants) splicing variant is associated with resistance to ARTA. Because the presence of AR-V7 does not affect the efficacy of other systemic therapies used in mCRCPs, particularly taxanes, AR-V7 is a candidate predictive biomarker for the individualisation of mCRCP treatment. Two types of assays based on mRNA or abnormal protein detection are used to detect AR-V7 in circulating tumour cells. Aim: To describe the current status of AR-V7 testing in mCRPC and possible applications of this method for predicting outcomes of ARTA therapy. Conclusion: The percentage of CTC AR-V7+ in ARTA-naive men is relatively low at baseline, but in patients pretreated with ARTA, the prevalence of AR-V7 increases to 19–34%. Given the relatively high expected prevalence, AR-V7 testing may be economically feasible in this population. The proportion of AR-V7+ patients responding to ARTA retreatment appears to be very low, at only 4.8%. AR-V7 testing could thus be useful if an ARTA switch is considered in a patient progressing onto an ARTA drug. Both protein-based tests and mRNA-based tests are currently undergoing clinical validation in prospective studies, with results expected within a year.
