The satisfactory reproducibility of the Ki-67 index in breast carcinoma, and it′s correlation with the recurrence score

Objective: The clinical utility of Ki-67 in predicting response to neoadjuvant chemotherapy is limited by lack of an accepted validated method of assessment of Ki-67 and wide variations in the cut-offs. In this study, the interobserver variability in the estimation of Ki-67 proliferation index (PI) and its association with recurrence score (RS) was assessed. Materials and Methods: The interobserver variability was assessed between 3 pathologists in 27 invasive breast carcinomas that had also been analyzed for the RS (Oncotype DX). The guidelines proposed by International Breast Cancer Working Group (IBCWG) for analysis of Ki-67 were used. A Pearson correlation between the mean Ki-67 PI and the RS was calculated. Results: In the 27 tumors, the pathologists were in 89.1% agreement (intra-class correlation coefficient = 0.891, 95%, 0.806-0.945) for Ki-67 PI estimation. Furthermore, a strong positive correlation between Ki-67 and RS (r = 0.78464, P < 0.0001) was obtained. There were 10 cases with low risk (mean RS: 10.1; Ki-67 range: 3-33%); 13 with intermediate risk (mean RS: 21.4; Ki-67 range: 6-43%) and 3 with high risk (mean RS: 53; Ki-67 range: 55-91%). Conclusion: Conventional evaluation of Ki-67 index is reproducible using the method suggested by the IBCWG. The wide range of Ki-67 PI in low and intermediate risk groups and the unexpectedly high Ki-67 PI in some low risk carcinomas limit its use as a predictive measure.