ERBB2 and breast carcinoma: <h4>Purpose</h4>The purpose of this study was to examine whether Ki67-scores have a predictive significance for pathological complete response (pCR) and invasive disease-free survival (IDFS) in HER2-positive breast cancer.<h4>Methods</h4>This retrospective, bi-centric cohort study focused on HER2-positive early breast cancer patients undergoing neoadjuvant chemotherapy from 2015 to 2023.