AIs have been found to have higher efficacy than Tamoxifen (Rugo 2008; Baum et al. 2003; Coombes et al. 2004; Goss et al. 2005; Gibson et al. 2009; Howell et al. 2005; Markopoulos 2010), and there is a general recommendation for the administration of an AI at some point during the adjuvant hormonal treatment of postmenopausal patients with hormone receptor positive early breast cancer (Burstein et al. 2010). The gene discussed is NR4A1; the disease is breast cancer.