ESR1 and breast cancer: Given that so far the IHC4 score has only been shown to be prognostic, the aims of this project were (i) to determine whether IHC4 score determined on pre-treatment core biopsies predicted response following neo-adjuvant chemotherapy in ER+ breast cancer; (ii) to determine whether IHC4 provided more predictive information than Ki67 alone, given that Ki67 has already been found to predict for pCR.