The poor prognostic features in breast cancer include hormone insensitivity, such as lack of estrogen receptor (ER), as well as overexpression of the epidermal growth factor (EGF) family of receptor tyrosine kinases, especially epidermal growth factor receptor (EGF-R, also, HER1 and erbB1) and HER2/neu (erbB2) [5]. The gene discussed is ESR1; the disease is breast cancer.