Fit-for-Purpose Ki-67 Immunohistochemistry Assays for Breast Cancer

• Published in: Laboratory investigation Vol. 104; no. 7; p. 102076
• Main Authors: Torlakovic, Emina E., Baniak, Nick, Barnes, Penny J., Chancey, Keith, Chen, Liam, Cheung, Carol, Clairefond, Sylvie, Cutz, Jean-Claude, Faragalla, Hala, Gravel, Denis H., Dakin Hache, Kelly, Iyengar, Pratibha, Komel, Michael, Kos, Zuzana, Lacroix-Triki, Magali, Marolt, Monna J., Mrkonjic, Miralem, Mulligan, Anna Marie, Nofech-Mozes, Sharon, Park, Paul C., Plotkin, Anna, Raphael, Simon, Rees, Henrike, Seno, H Rommel, Thai, Duc-Vinh, Troxell, Megan L., Varma, Sonal, Wang, Gang, Wang, Tao, Wehrli, Bret, Bigras, Gilbert
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2024
• Subjects: breast cancer; clinical utility; fit-for-purpose; Ki-67 immunohistochemistry assay; fit-for-purpose; Ki-67 immunohistochemistry assay; breast cancer; clinical utility
• ISSN: 0023-6837; 1530-0307; 1530-0307
• DOI: 10.1016/j.labinv.2024.102076

New therapies are being developed for breast cancer, and in this process, some “old” biomarkers are reutilized and given a new purpose. It is not always recognized that by changing a biomarker’s intended use, a new biomarker assay is created. The Ki-67 biomarker is typically assessed by immunohistochemistry (IHC) to provide a proliferative index in breast cancer. Canadian laboratories assessed the analytical performance and diagnostic accuracy of their Ki-67 IHC laboratory-developed tests (LDTs) of relevance for the LDTs’ clinical utility. Canadian clinical IHC laboratories enrolled in the Canadian Biomarker Quality Assurance Pilot Run for Ki-67 in breast cancer by invitation. The Dako Ki-67 IHC pharmDx assay was employed as a study reference assay. The Dako central laboratory was the reference laboratory. Participants received unstained slides of breast cancer tissue microarrays with 32 cases and performed their in-house Ki-67 assays. The results were assessed using QuPath, an open-source software application for bioimage analysis. Positive percent agreement (PPA, sensitivity) and negative percent agreement (NPA, specificity) were calculated against the Dako Ki-67 IHC pharmDx assay for 5%, 10%, 20%, and 30% cutoffs. Overall, PPA and NPA varied depending on the selected cutoff; participants were more successful with 5% and 10%, than with 20% and 30% cutoffs. Only 4 of 16 laboratories had robust IHC protocols with acceptable PPA for all cutoffs. The lowest PPA for the 5% cutoff was 85%, for 10% was 63%, for 20% was 14%, and for 30% was 13%. The lowest NPA for the 5% cutoff was 50%, for 10% was 33%, for 20% was 50%, and for 30% was 57%. Despite many years of international efforts to standardize IHC testing for Ki-67 in breast cancer, our results indicate that Canadian clinical LDTs have a wide analytical sensitivity range and poor agreement for 20% and 30% cutoffs. The poor agreement was not due to the readout but rather due to IHC protocol conditions. International Ki-67 in Breast Cancer Working Group (IKWG) recommendations related to Ki-67 IHC standardization cannot take full effect without reliable fit-for-purpose reference materials that are required for the initial assay calibration, assay performance monitoring, and proficiency testing.