ESR1 and breast cancer: Invasive breast cancer, from stage IIB to stage IIIC, all subtypes are included, either HR (ER, PR)-positive or -negative, HER2-positive or -negative, eligible to neoadjuvant systemic therapy.Neoadjuvant systemic treatment composed of anthracyclines-based chemotherapy and taxanes, trastuzumab for HER2-positive patients.