Gene expression profile (GEP) assays (e.g. Prosigna, Endopredict and Oncotype) have an important role in Estrogen Receptor (ER)pos/HER2neg BC as they inform the physician and patient on the risk of early recurrence and to assist them to choose the best treatment option in order to avoid recurrences but also useless treatments, in fact, this group of BC is a very heterogeneous disease and GEP might help to provide tailored treatment [32]. This evidence concerns the gene ESR1 and breast cancer.