Over the last 10–15 years, aromatase inhibitors (AIs) have been shown to be better than tamoxifen in multiple clinical scenarios in breast cancer including the neoadjuvant setting (Dixon et al, 2000, 2001; Nabholtz et al, 2000; Eiermann et al, 2001; Mouridsen et al, 2001; Baum et al, 2002; Thurlimann et al, 2005; Crivellari et al, 2008; Ellis et al, 2011). The gene discussed is CYP19A1; the disease is breast carcinoma.