ESR1 and breast carcinoma: Interestingly, recent findings suggest that the Magee Equation [46], another inexpensive tool that is based on ER, PR, HER2, and KI67 in addition to the Nottingham score and tumor size, can be used to predict pathologic response to neoadjuvant chemotherapy in ER + /HER2-negative/equivocal breast cancer [47].