ESR1 and breast cancer: Therapy management of breast cancer depend on its histological and molecular characteristics, based primarily on the expression of estrogen receptors (ERs), progesterone receptor (PR) and ERBB2 receptor (HER2), which allow to distinct the breast carcinoma in diverse molecular subtypes (i.e., Luminal A and B, Her2-enriched, Basal- and Normal-like, ER-negative and Triple-Negative Breast Cancers, TNBC) [3].