ABSTRACTObjective: To determine the predictive value of Ki67 on pathological complete response (pCR) of breast and axilla regions inbreast cancer (BC) patients receiving neoadjuvant therapy (NAT).Study Design: Descriptive study.Place and Duration of the Study: Departments of Medical Oncology, Sirnak State Hospital, Aydin State Hospital, Manisa CelalBayar University, and Dokuz Eylul University, from November 2010 to July 2022.Methodology: PCR and various histopathological parameters were evaluated for BC patients receiving NAT. The Youden Indexmethod was used to find the cut-off value for the Ki67 variable according to the receiver operating characteristic (ROC) curve.This value was obtained as 77.5. Breast and axillary responses were individually evaluated to assess response to NAT. Univariateand multivariate logistic regression analysis were used to predict both breast and axillary pCR.Results: A total number of 280 females receiving NAT for BC were included in the study. Multivariate analysis for breast pCR toNAT showed that Ki67 index (>77.5 vs <77.5, p=0.047) was statistically significant marker. While Ki67 index was significant forbreast pCR in both univariate and multivariate analyses, the same was not observed on axillary response (p=0.387).Conclusion: High Ki67 level was significantly associated with breast pCR in BC patients receiving NAT, but a similar effect wasnot observed on axillary pCR. These findings suggest that breast and axilla tissues have a biological differences in treatmentresponses.Key Words: Axillary response, Breast cancer, Ki67 Labeling Index, Neoadjuvant therapy, pathological complete response.</p
