AR and neoplasm: Hallmark characteristics of CRPC tumours include, but are not limited to: Increased levels of AR or its mRNA [17,51,52]; somatic mutations in the AR sequence (such as T877A) that convert anti-androgen drugs into agonists [51]; upregulation of enzymes responsible for androgen synthesis [53]; direct alteration of the AR gene [54]; and constitutive transcriptional activity of truncated AR splice variants [55–59] (discussed in Section 3).