At present, there is a certain negative conversion rate of HER2 in non-pCR patients after neoadjuvant treatment with trastuzumab, and it is controversial whether postoperative adjuvant treatment should be intensified for the negative conversion population.[6] The aim of this study was to analyze the clinicopathological data of 499 patients with HER2-positive breast cancer and to investigate the changes in HER2 expression status in patients with HER2-positive breast cancer after neoadjuvant treatment. This evidence concerns the gene ERBB2 and breast cancer.