Comparison of 5 Ki-67 antibodies regarding reproducibility and capacity to predict prognosis in breast cancer: does the antibody matter?

Summary Although several antibodies are available for immunohistochemical detection of Ki-67, even the most commonly used MIB-1 has not been validated yet. Our aim was to compare 5 commercially available antibodies for detection of Ki-67 in terms of agreement and their ability in predicting prognosis of breast cancer. Tissue microarrays were constructed from 378 breast cancer patients' representative formalin-fixed, paraffin-embedded tumor blocks. Five antibodies were used to detect Ki-67 expression: MIB-1 using chromogenic detection and immunofluorescent-labeled MIB-1, SP-6, 30-9, poly, and B56. Semiquantitative assessment was performed by 2 pathologists independently on digitized slides. To compare the 5 antibodies, intraclass correlation and concordance correlation coefficient were used. All the antibodies but immunofluorescent-labeled MIB-1 (at 20% and 30% thresholds, P =.993 and P =.342, respectively) and B56 (at 30% threshold, P =.288) separated high- and low-risk patient groups. However, there were a significant difference ( P values for all comparisons≤.005) and a moderate concordance (intraclass correlation, 0.645) between their Ki-67 labeling index scores. The highest concordance was found between MIB-1 and poly (concordance correlation coefficient=0.785) antibodies. None of the antibodies except Ki-67 labeling index as detected by poly ( P =.031) at 20% threshold and lymph node status ( P P