ESR1 and breast cancer: In early breast cancer (stage I-II-III) patients, the knowledge of the clinical and biological prognostic factors [Tumor size, lymph node status, Grading, Estrogen Receptor (ER) and Progesterone Receptor (PgR) status, proliferative index (Ki67 value) and HER2 status] is very important in order to identify the most appropriate treatment options and decide about the start of NAT or refer the patient directly to the surgeon considering later an adjuvant therapy.