Specifically, National Comprehensive Care Network (NCCN) guidelines for the treatment of invasive breast cancer outline systemic adjuvant therapies based on hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) statuses, where positive HR status is defined as expression of the estrogen (ER) and/or progesterone (PR) receptors 2. This evidence concerns the gene ESR1 and invasive breast carcinoma.