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Fit-for-Purpose Ki-67 Immunohistochemistry Assays for Breast Cancer
Emina E Torlakovic1, Nick Baniak2, Penny J Barnes3
1Department of Pathology and Laboratory Medicine and Canadian Biomarker Quality Assurance, University of Saskatchewan and Saskatchewan Health Authority, Saskatoon, Saskatchewan, Canada.
Canadian labs evaluated Ki-67 immunohistochemistry (IHC) assays for breast cancer, finding significant variability in analytical performance. Poor agreement for 20% and 30% cutoffs highlights the need for standardized protocols and reference materials for reliable Ki-67 testing.
Area of Science:
- Oncology
- Pathology
- Biomarker Analysis
Background:
- Ki-67 immunohistochemistry (IHC) is crucial for assessing breast cancer proliferation.
- Reutilization of biomarkers like Ki-67 for new purposes necessitates validation of laboratory-developed tests (LDTs).
- Standardization of Ki-67 IHC assays remains a challenge despite international efforts.
Purpose of the Study:
- To assess the analytical performance and diagnostic accuracy of Ki-67 IHC LDTs in Canadian laboratories.
- To evaluate the clinical utility of these Ki-67 assays based on their performance.
- To identify factors contributing to variability in Ki-67 testing.
Main Methods:
- Canadian clinical IHC laboratories participated in a quality assurance pilot run for Ki-67 breast cancer testing.
- In-house Ki-67 IHC assays were performed on provided breast cancer tissue microarrays.
- Assay results were analyzed using QuPath software and compared against the Dako Ki-67 IHC pharmDx reference assay.
- Positive percent agreement (PPA) and negative percent agreement (NPA) were calculated for 5%, 10%, 20%, and 30% cutoffs.
Main Results:
- Significant variability in analytical sensitivity and diagnostic accuracy was observed among participating laboratories.
- Agreement was better for lower cutoffs (5% and 10%) compared to higher cutoffs (20% and 30%).
- Only 4 out of 16 laboratories demonstrated robust IHC protocols with acceptable PPA across all cutoffs.
- Poor agreement was attributed to IHC protocol conditions rather than the image analysis readout.
Conclusions:
- Canadian clinical Ki-67 IHC LDTs exhibit wide analytical sensitivity ranges and poor agreement, particularly at higher cutoffs.
- Standardization efforts are hindered by inconsistent IHC protocols and a lack of fit-for-purpose reference materials.
- Reliable reference materials are essential for assay calibration, performance monitoring, and proficiency testing to ensure accurate Ki-67 assessment in breast cancer.
