While re-activation of the AR is undoubtedly the hallmark of progression to CRPC, it is also clear that the ability of PCa tumor cells to retain some degree of phenotypic plasticity, or the ability to change into a variety of aggressive tumor cell types, such as cancer stem cells or cells that have undergone epithelial to mesenchymal transition (EMT), is also a critical component of advanced disease. This evidence concerns the gene AR and neoplasm.