ESR1 and breast cancer: Given the prognostic value of biomarkers expression and its important role for deciding treatment scheme, the aim of this study was to compare the IHC expression of ER, PR, HER2, and Ki67 in core-needle biopsies and surgical excision specimens in NAT-treated and non-treated breast cancer samples from patients diagnosed in the Colombian National Cancer Institute (NCI), in order to evaluate NAT effect on biomarker expression profile.