The effect of Ki67 visual scale to improve accuracy of Ki67 index estimation in breast cancer

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Padol Chamninawakul


Background: The Ki67 index is an important prognostic marker in breast cancer. The current Ki67 index estimation by unaided optical microscope is widely criticized on the grounds of high inter-observer and intra-observer variability. For more accurate assessment, we create the Ki67 visual scale by using the figure from digital image analysis. The aims of this study were to validate the effect of Ki67 visual scale to improve accuracy of Ki67 index estimation in breast cancer.

Methods: This is an experimental study including 30 cases diagnosed with invasive breast carcinoma. The Ki67 index was determined using DIA. Manual Ki67 scoring by VE was performed with and without the aid of Ki67 visual scale sheet. Inter-observer agreements between Ki67 index by VE (with and without Ki67 visual scale) and by DIA were assessed using Kendall’s correlation coefficients and scatterplots.

Results: Correlation for inter-observer agreement between VE without scale sheet and DIA reveals an almost perfect agreement with a Kendall’s correlation coefficient of 0.826 (p < 0.01) whereas the correlation between VE with scale sheet and DIA also reveals an almost perfect agreement but with a Kendall’s correlation coefficient of 0.950 (p < 0.01). Although the correlation coefficients of both comparisons similarly reveal an almost perfect agreement, the correlation for inter-observer agreement between VE with scale sheet and DIA was even higher.

Conclusions: Ki67 visual scale would appear to improve accuracy and reproducibility of Ki67 index estimation using optical microscope in breast cancer patients. Such study would help define a practical tool for more standardized Ki67 index estimation by optical microscope.


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