AR and neoplasm: Several potential mechanisms of resistance have been investigated in the past, including the upregulation of multi-drug resistance (MDR) transporters [7] and the upregulation of phosphorylated AKT [8], with a potential predictive role for the detection of intranuclear androgen receptor splice variant 7 (AR-v7) in circulating tumor cells [9,10]; however, no biomarker of taxane resistance or response for patients with mCRPC has been validated for clinical decision-making.