Abstract P5-02-03: A comparison of the hot spot and the average cancer cell counting methods and the optimal cut-off point of the Ki-67 index for luminal type breast cancer with or without recurrence – A case control study for prognostic factors

Abstract

Abstract Background: Uncontrolled proliferation is a key factor of malignant tumors. The Ki-67 index is known to be a significant prognostic factor in terms of disease-free and overall survival in breast cancer. However, there are several limitations in the use of this biomarker, the biggest being a difference in opinion among breast cancer specialist on how to create an international standard for the Ki-67 index. Therefore, the aim of this case control study was to investigate the most suitable area to count and to determine the optimal cut-off point of the Ki-67 index for a more accurate prognosis. Patients and Methods: Thirty recurrent cases (< 5 years after initial treatment) were selected among hormone receptor (HR)-positive/HER2-negative breast cancer patients. As a control, 90 non-recurrent cases (>5 years after initial treatment) were randomly selected by allotting 3 controls to each recurrent case based on the following predetermined criteria; age, nodal status and tumor size. All patients were treated with adjuvant endocrine therapy alone. Both the hot spot and the average area of the tumor were evaluated on a Ki-67 immunostaining slide and then photographs were taken. The Ki-67 index was automatically scored using the CountσCell (Seiko Tech., Fukuoka, Japan). Moreover, the difference in the Ki-67 index values (ΔKi-67) between the hot spot and the average area were calculated. The Chi-square and Fisher’s exact tests were used for inter-group comparison. Paired t-test and Wilcoxon’s (non-parametric) test were used to compare the mean value for the Ki-67 index values. Logistic regression analysis was used to calculate the odds ratio of the Ki-67 index related to recurrence. Results: 1) A higher Ki-67 index value at the hot spot was more significantly associated with recurrence than the average area, and the Ki-67 index value of 20% at the hot spot was the most suitable cut-off point for predicting recurrence. Irrespective of the area counted, the Ki-67 index value was significantly higher in all of the recurrent cases (p<0.0001). The next step was to determine the most suitable cut-off point for the Ki-67 index. Out of all the cut-off points used in this study, the most significant difference was found in the values 20, 25 and 30% at only the hot spot (each p<0.0001). Furthermore, logistic regression analysis demonstrated that the highest odds ratio was 20% at the hot spot. 2. The ΔKi-67 index value was significantly correlated with recurrence and the ΔKi-67 index value of 10% was the most suitable cut-off point. The ΔKi-67 index values ranged from 2 to 54% (median: 10%) and significantly correlated with recurrence and the Ki-67 value at hot spot (p<0.0001). Logistic regression analysis revealed that a ΔKi-67 index cut-off point of 10%. Conclusion: A higher Ki-67 index value at the hot spot was strongly correlated with recurrence, and the most suitable cut-off point was 20%. ΔKi-67 index value also significantly correlated with recurrence, and the most suitable cut-off point was 10%. Finally, the hot spot counting method is strongly related to tumor biology and prognosis in HR-positive/HER2-negative breast cancer. Citation Format: Nobuyuki Arima, Reiki Nishimura, Tomofumi Osako, Yasuyuki Nishiyama, Yasuhiro Okumura, Masahiro Nakano, Mamiko Fujisue, Rumiko Tashima, Yasuo Toyozumi. A comparison of the hot spot and the average cancer cell counting methods and the optimal cut-off point of the Ki-67 index for luminal type breast cancer with or without recurrence – A case control study for prognostic factors [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-02-03.