Abstract PD06-07: Evaluation of an optimal cut-off point for the Ki-67 index as a prognostic factor in primary breast cancer.

Abstract

Abstract Background: The proliferation biomarker Ki-67 is considered to be a prognostic factor for breast cancer and has been investigated in several studies. However, there is no standard cut-off point for the Ki-67 index. Therefore, we retrospectively investigated an optimal cut-off point in terms of the prognostic factor in primary breast cancer. Patients&Methods: Immunohistochemical (IHC) analysis of the proliferation marker Ki-67 index was performed on 4338 patients with primary breast cancer until March 2012 at Kumamoto City Hospital. Out of these patients, there were 2375 consecutive cases with ER and/or PgR positive and HER2 negative tumors since 1997. Items examined were ER, PgR, HER2, tumor size, nodal status, nuclear grade, and p53 overexpression. The Kaplan-Meier test was used to calculate prognosis (cumulative disease-free survival (DFS) and overall survival (OS)) and tested with the log-rank procedure. Cox's proportional hazard model was used to perform a univariate and multivariate analyses of the factors related to DFS. In addition, an analysis was conducted to determine various cut-off values for the Ki-67 index. Results: The median Ki-67 value was 21%, with a mean of 26.2%. Univariate and multivariate analysis revealed that the Ki-67 index was an independent prognostic factor for DFS and OS. A multivariate analysis revealed the following hazard ratio (HR) and cut-off values for the Ki-67 index; HR was 1.92 in cases with a cut-off value of 20%, 1.91 in 35%, 1.87 in 40%, 1.89 in 45% and 1.79 in 50%, respectively. These findings suggested that the optimal cut-off point was 20%. In the cases with luminal type (ER and/or PgR positive and HER2 negative) breast cancer, a higher Ki-67 value (20% ≤) correlated with larger tumor size, positive nodes, higher grade, and overexpression of p53. Moreover, patients with a higher Ki-67 value showed significantly lower DFS/OS rates. A multivariate analysis also revealed that the Ki-67 index is a significant prognostic factor in luminal type breast cancer. Conclusion: The optimal cut-off value for the Ki-67 index is 20%. Moreover, this proliferation marker is a significant prognostic factor in evaluating primary breast cancer. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD06-07.