AR and neoplasm: cfDNA detectable AR amplification has been reported as a biomarker predicting therapeutic resistance to second generation anti-androgens (abiraterone/enzalutamide) in several studies [23, 52, 53], while circulating tumor cell (CTC) detectable ligand independent AR splice variant (AR-V7) has been reported as predictive of abiraterone/enzalutamide resistance and taxane chemotherapy sensitivity [63, 64].