Next, with the aim of comparing the observed gene expression changes following estrogen deprivation in breast cancer cells to patients who received aromatase inhibitor (AI) treatment, we analysed a publicly available array data set consisting of 58 postmenopausal breast cancer patients with array profiles assessed before and after neoadjuvant treatment with letrozole (Gene expression omnibus number: GSE5462)[26]. The gene discussed is CYP19A1; the disease is breast cancer.