Abstract Purpose This study was conducted to analyze the Ki-67 expression before and after neoadjuvant chemotherapy and clinical pathology characteristics of different biological breast cancer phenotypes at our center. A correlation study was performed between Ki-67 index change and the prognosis of different biological breast cancer phenotypes and prognosis in Northern China. Methods A regression analysis was performed on 213 patients with invasive breast carcinoma accepted NAC admitted to Tianjin Medical University Cancer Institute and Hospital of Breast Surgery from January 2007 to April 2008. These patients were subtyped by hormone receptor status and HER2 status.The Ki67 index (percentage of Ki67-positive cancer nuclei) were determined immunohistochemically. The prognostic value of the Ki-67 index for different biological breast cancer phenotypes disease-free survival (DFS) and overall survival (OS) was investigated by use of Kaplan–Meier curves and multivariable Cox regression. Results The overall pathologic CR (pCR) rate, defined as no invasive residuals in breast and axilla, was 17.8%. The highest pCR rate of 32.1% was observed in patients with HR-/HER2+ tumors, which is 11.4%, 20.0% and 26.2% in HR+/HER2- HR+/HER2-,HR+/HER2+and HR-/HER2- tumor respectively(P = 0.024).The Ki-67 expression of pre-NAC and post-NAC have prognostic significance in HER2- breast cancer, which have not significance different in HER2+ breast cancer:The best Ki-67 idex cut point of pre-NAC and post-NAC to predict long-term survival was respectively 20% and 10% in HR+/HER2- breast cancer. Moreover, patients with a higher Ki-67 index (> cut-off point) showed significantly lower 5year-DFS/OS rates compared with those whose Ki-67 index were below cut-off point. In addition, Ki-67 index of post-NAC were independent prognostic factors for 5 year disease-free survival of patients with HR+/HER2- breast cancer. Ki-67 change between pre- and post-NAC as an independent prognostic factor independently predict prognosis in the patients who have not achieved pCR, while the best cut-off point was 18%. Conclusion The Ki-67 index of pre- and post-NAC could predict the prognosis in the patients with HER2- breast cancer. Moreover, the Ki-67 change between pre- and post-NAC was an independent prognostic factor in the patients who have not achieved pCR. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-08-05.