Ki67 assessment in invasive luminal breast cancer: a comparative study between different scoring methods

Abstract

Background: Ki67 reflects the proliferation activity in breast cancer (BC). However, an optimal method for its assessment in clinical settings has yet to be robustly defined. In this study we compared several methods to score Ki67 to identify a reliable and reproducible method for routine practice. Methods: Sections from luminal BC cohort (n = 1662) were immunohistochemically stained with Ki67 and were assessed for the percentage, pattern, and intensity of expression. Ki67 positivity was evaluated using three methods: (i) quantification of Ki67positive cells among 1000 invasive tumour cells within hotspot, (ii) average estimation of Ki67 within a defined hotspot, and (iii) average estimation of Ki67 positivity within the whole section. Time required for scoring, interobserver agreement and association with outcome were determined. Results:The mean percentage of Ki67 expression per 1000 cells method was 16%, while the mean value of Ki67 scores using the average estimation within hotspot and whole slide were 14% and 12%, respectively. Quantification of Ki67-positive cells within 1000 cells had the highest degree of consistency between observers, and the highest hazard ratio predicting patient outcome when compared to using different common Ki67 cutoffs, which was independent of the other two methods. Granular pattern of Ki67 expression was associated with poorer outcome as compared to the other patterns. Conclusion: Assessment of Ki67 expression using quantification positive cells among 1000 tumour cells is an optimal method to achieve high reliability and reproducibility. Comment on the predominant Ki67 expression pattern would add prognostic and predictive value in luminal BC.

The clinical value of progesterone receptor expression in luminal breast cancer: A study of a large cohort with long‐term follow‐up

“…The median time of follow-up is 125 months (range, 2-257 months). Ki67 expression levels, as assessed in full face sections, using the standard methodology as previously published, 21,22 were available and were used for comparative analysis with PR. Adjuvant endocrine therapy was offered to 90% (n = 1715 of 1904) patients included in the study, whereas 189 patients (10%) did not receive endocrine therapy.…”

Evaluation oncotype DX® 21‐gene recurrence score and clinicopathological parameters: a single institutional experience

“…The IHC staining was performed automatically using the clinically validated Dako Cytomation EnVision+ detection system, according to the standard protocols using primary antibody (anti-human Ki67 monoclonal antibody MIB1; Dako, Glostrup, Denmark). 25 Ki67 was visually assessed by an experienced pathologist (A.L.) with eyeball examination of the IHCstained sections using a light microscope.…”

“…The percentage of Ki67 expression level was assessed by counting Ki67-stained cells in 1000 invasive tumour cells in hot-spots, as previously published. 25,26…”

“…Ki67 was assessed on full‐face sections ( n = 302), which were prepared from the same FFPE tissue blocks that were used for Oncotype DX testing. The IHC staining was performed automatically using the clinically validated Dako Cytomation EnVision+ detection system, according to the standard protocols using primary antibody (anti‐human Ki67 monoclonal antibody MIB1; Dako, Glostrup, Denmark) 25 . Ki67 was visually assessed by an experienced pathologist (A.L.)…”

“…with eyeball examination of the IHC‐stained sections using a light microscope. The percentage of Ki67 expression level was assessed by counting Ki67‐stained cells in 1000 invasive tumour cells in hot‐spots, as previously published 25,26 …”