Concordance of HER2 Immunohistochemistry and Fluorescence In Situ Hybridization Using Tissue Microarray in Breast Cancer

Aim: Immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) are common methods for assessment of human epidermal growth factor receptor 2 (HER2) in breast cancer. Materials and Methods: In a cohort of 498 consecutive patients with breast cancer, we examined concordance between IHC and FISH for HER2 on tissue microarray (TMA) sections. In a subset of 116 specimens, we examined HER2 concordance from the block used for diagnostics and a randomly-chosen additional block (a proxy of the core biopsy). Results: Overall concordance between both methods on TMA sections was 93.8% and between HER2, determined on diagnostic and additional blocks, was 93.6% for IHC and 98.0% for FISH. Conclusion: Since some cases were discordant, we suggest that both methods be used for HER2 assessment. The lower concordance rate between diagnostic and additional blocks using IHC compared to FISH suggests a greater variability of IHC staining across tumor regions than for FISH results.

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