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). This evidence concerns the gene CYP19A1 and breast cancer.