The androgen receptor (AR) plays a role in the pathogenesis of prostate cancer and can be expressed in invasive breast cancer (Itkonen and Mills 2012; Gonzalez et al 2008). AR is the product of the AR gene, which is located on the X chromosome. AR is in the nuclear receptor superfamily and is part of the steroid receptor family, and it has a six-region structure with a defined functional domain (Itkonen and Mills 2012).
Amplification of the AR gene and AR mutations occur in 30% and 1-30% of castration-resistant prostate cancer, respectively (Waltering et al. 2012). AR expression is measured using immunohistochemistry (IHC), and is detectable in the majority of castration-resistant prostate cancer (Linja et al. 2001; Waltering et al. 2012) and 75% of invasive breast cancers (Collins et al. 2011; Gonzalez et al 2008).