In the PeriOperative Endocrine Therapy for Individualizing Care (POETIC) trial, this knowledge is expanded upon where patients with primary breast cancer are biopsied before and after 2 weeks on either a non-steroidal aromatase inhibitor or no treatment to identify novel biomarkers for response (Dowsett et al. 2011b). This evidence concerns the gene CYP19A1 and breast carcinoma.