Comparative Analysis of Equivocal (2 +) and Positive (3 +) HER2 Immunohistochemistry (IHC) and Bright-Field Dual-Color In Situ Hybridization (DISH) in Primary Breast Cancer - Study Summary

Sep 28, 2026

HER2 serves as a key predictive and prognostic biomarker in breast cancer, and HER2 testing guides targeted therapy decisions. This retrospective single-center cohort evaluates agreement between HER2 immunohistochemistry (IHC 2 +/3 +) and bright-field dual-color in situ hybridization (DISH) using nationwide referral specimens from 1,307 node-positive primary cases. DISH identified HER2 amplification in 933 cancers and showed no significant differences versus published IHC-FISH meta-analysis data, supporting DISH as a reliable, more accessible alternative to FISH.

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Comparative Analysis of Equivocal (2 +) and Positive (3 +) HER2 Immunohistochemistry (IHC) and Bright-Field Dual-Color In Situ Hybridization (DISH) in Primary Breast Cancer From 1,307 Node-Positive Patients Kroonpong Iampenkhae 1,2, Adiluck Pisutpunya3, Chawinthorn Vuthithammee 1,2, Piyakawin Sodsoon 1,2 and Sompon Apornvirat4 Breast Cancer: Basic and Clinical Research Volume 19: 1-6 © The Author(s) 2025 Article reuse guidelines: [sagepub.com/journals-permissions](sagepub.com/journals-permissions)[ ](sagepub.com/journals-permissions)[DOI: 10.1177/11782234251407914](DOI: 10.1177/11782234251407914)[ ](DOI: 10.1177/11782234251407914)[journals.sagepub.com/home/bcb](journals.sagepub.com/home/bcb) Abstract Background: Human epidermal growth factor receptor 2 (HER2) is an important predictive and prognostic biomarker in breast cancer. Immunohistochemistry (IHC) is the preferred initial test due to its cost-effectiveness and simplicity. While fluorescence in situ hybridization (FISH) is the traditional gold standard test for HER2 gene amplification, DISH has emerged as an accepted alternative that allows evaluation under a standard light microscope. Objectives: To evaluate agreement between HER2 IHC (2 +/3 +) and DISH in node-positive primary breast cancersand compare findings with published IHC and FISH data. Design: Retrospective single-center cohort study using nationwide referral specimens. Methods: Cases of pathologically confirmed lymph node metastasized invasive breast carcinoma with HER2 IHC scores of 2 + and 3 + were retrieved. Interpretation of HER2 IHC was performed using the 2023 ASCO/CAP guideline. HER2 DISH was conducted and evaluated by the HER2/CEP17 signal ratio on primary tumors first, and on metastasized lymph nodes in cases of persistent technical failure. Results: Among 1,307 breast cancers, DISH detected HER2 amplification in 933 cases, including 92%(760) of IHC 3 + cases and 36%(173) of IHC 2 + cases. Seven cases with persistent technical failure on primary tumors were resolved when switching to lymph node specimens. Comparison with the meta-analysis data of IHC and FISH showed no significant differences, indicating that DISH is a reliable alternative to FISH. Conclusion: Our study demonstrates a high concordant rate between HER2 IHC and DISH in the IHC 3 + group anda low positive rate in the IHC 2 + group. We found no significant difference in the positive rates of HER2 IHC to DISH when compared with prior data of IHC to FISH, reaffirming the use of HER2 DISH as an effective and more accessible alternative to FISH in HER2 2 +/3 + breast cancer. Keywords HER2, breast neoplasms, immunohistochemistry, in situ hybridization, result reliability Received: 3 June 2025; accepted: 1 December 2025 1 Department of Pathology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand 2King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Bangkok, Thailand 3Department of Pathology, Faculty of Medicine, Thammasat University, Pathum Thani, Thailand 4Chulabhorn International College of Medicine, Thammasat University, Pathum Thani, Thailand Corresponding author: Sompon Apornvirat, Chulabhorn International College of Medicine, Thammasat University, 99 Moo 18, Paholyothin Road, Klongnung, Klongluang, Pathum Thani 12120, Thailand. Email: [Somponap@tu.ac.th](Somponap@tu.ac.th) Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License ([https://creativecommons.org/licenses/by-nc/4.0/](https://creativecommons.org/licenses/by-nc/4.0/)) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages ([https://us.sagepub.com/en-us/nam/open-access-at-sage](https://us.sagepub.com/en-us/nam/open-access-at-sage)). Introduction The human epidermal growth factor rece

FAQs

Why is HER2 testing important in breast cancer?

HER2 is an important predictive and prognostic biomarker, and HER2 status helps determine response to HER2-targeted therapy.

What is the main purpose of comparing HER2 IHC with DISH?

To evaluate agreement between HER2 IHC (2 +/3 +) and DISH in node-positive primary breast cancers and compare results with published IHC and FISH data.

What did the study find about DISH compared with FISH-based reference data?

The study reported no significant differences versus meta-analysis IHC-FISH data, indicating DISH is a reliable alternative to FISH.

Sep 28, 2026

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