Comparison of visual assessment and image analysis in the evaluation of Ki-67 expression and their prognostic significance in immunohistochemically defined luminal breast carcinoma

OBJECTIVES To compare the Ki-67 labeling index value obtained through immunohistochemistry analysis by human examiners to that obtained from computer-assisted image analysis, and to establish a cut-off value for Ki-67 labeling index for each method in luminal B breast carcinoma. METHODS Immunohistochemistry analysis for Ki-67 was performed on the formalin-fixed, paraffin-embedded tissue samples from 403 patients with primary luminal breast cancers. Whole slide images were obtained using the NanoZoomer (Hamamatsu Photonics, Hamamatsu, Japan) and thoroughly analyzed using the Definiens Tissue Studio version 1.1 (Definiens AG, Munich, Germany) to detect the percentage of positively-stained nuclei of carcinoma cells. RESULTS Although a significant correlation was found between the Ki-67 labeling index obtained by manual assessment and computer-assisted image analysis (Spearman rank correlation coefficient, P