AR and neoplasm: Until now, several studies have shown that the profiling of CTCs or cell-free tumor DNA (cfDNA) in liquid biopsies enables the detection of AR splice variants, AR copy number gains and AR mutations, all of whom are at least associated with enzalutamide resistance and poorer prognosis (Schwarzenbach et al. 2009, Antonarakis et al. 2014, Diaz & Bardelli 2014, Salvi et al. 2016, Wyatt et al. 2016, Conteduca et al. 2017).