Assessment of Ki67 in Breast Cancer: A Comparison Between the Eye-10 Method, Stepwise Counting Strategy, and International System of Ki67 Evaluation

Background & Objective: Ki-67 evaluation is an essential tool to define luminal A and B breast cancers, which is not yet systematized. The International Ki67 in Breast Cancer Working Group suggests the counting of 500 or 1000 cancer cells, which is a time-consuming process. Therefore, novel methods, such as the Eye-10 method and stepwise counting strategy, are proposed to facilitate measurement.   Methods: Immunohistochemical staining of Ki67 was performed on 100 hormone-receptor-positive invasive ductal carcinoma specimens. Ki67LI was evaluated for each case, and then results were dichotomized by a cut-off point of 20%. Next, for each sample, an expert pathologist visually assessed percentages of Ki67-positive cells in 10% intervals at a glance (Eye-10 method). Finally, by using a dynamic process with rejection regions, Ki67 was defined so if the estimate belonged to the upper or lower rejection region, the Ki67 status had been determined and if the rejection region could not be reached after counting the maximum number of 400 tumor cells, the specimen was regarded as equivocal (stepwise counting strategy). Results: The comparison between Eye-10 and Ki67LI revealed almost perfect agreement (kappa coefficient =0.889), and the concordance between the stepwise counting strategy and Ki67LI was substantial (kappa coefficient =0.639). Conclusion: Both two methods left some results in the gray/intermediate zone, which is unavoidable. Both methods are much faster and simpler than evaluation of Ki67LI and are also reliable. Regarding the gray zone in both methods, further improvements in the methodology, as well as more analytical studies, are needed.