ESR1 and neoplasm: Despite the presence of some factors predicting the response to neoadjuvant chemotherapy such as tumor size, histological grade or stage, molecular subtype, Ki-67 proliferation index, Her-2 status, PR status, and ER status [20,21,22,23], there is an urgent need for the identification of more reliable and readily accessible predictive and/or prognostic factors of response to neoadjuvant chemotherapy with a high possibility to be carried out in routine clinical practice and consequently, better adjustments for the therapy for each individual patient.