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Interobserver variation in the assessment of immunohistochemistry expression levels in HER2-negative breast cancer : can we improve the identification of low levels of HER2 expression by adjusting the criteria? An international interobserver study

Journal Contribution - Journal Article

The classification of human epidermal growth factor receptor 2 (HER2) expression is optimized to detect HER2-amplified breast cancer (BC). However, novel HER2-targeting agents are also effective for BCs with low levels of HER2. This raises the question whether the current guidelines for HER2 testing are sufficiently reproducible to identify HER2-low BC. The aim of this multicenter interna-tional study was to assess the interobserver agreement of specific HER2 immunohistochemistry scores in cases with negative HER2 results (0, 1+, or 2+/in situ hybridization negative) according to the current American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines. Furthermore, we evaluated whether the agreement improved by redefining immuno-histochemistry (IHC) scoring criteria or by adding fluorescent in situ hybridization (FISH).We conducted a 2-round study of 105 nonamplified BCs. During the first assessment, 16 pathol-ogists used the latest version of the ASCO/CAP guidelines. After a consensus meeting, the same pathologists scored the same digital slides using modified IHC scoring criteria based on the 2007 ASCO/CAP guidelines, and an extra "ultralow" category was added.Overall, the interobserver agreement was limited (4.7% of cases with 100% agreement) in the first round, but this was improved by clustering IHC categories. In the second round, the highest reproducibility was observed when comparing IHC 0 with the ultralow/1+/2+ grouped cluster
ISSN: 1530-0285
Issue: 1
Volume: 36
Publication year:2023