Indian Journal of Pathology and Microbiology
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Year : 2021  |  Volume : 64  |  Issue : 4  |  Page : 677-682

HER2 testing by immunohistochemistry in breast cancer: A multicenter proficiency ring study

1 Department of Pathology, Faculty of Medicine, Universiti Kebangsaan Malaysia Medical Centre, Kuala Lumpur, Malaysia
2 Department of Community Health, Faculty of Medicine, Universiti Kebangsaan Malaysia Medical Centre, Kuala Lumpur, Malaysia
3 Department of Pathology, Hospital Kuala Lumpur, Kuala Lumpur, Malaysia
4 Department of Pathology, University Malaya Medical Centre, Lembah Pantai, Kuala Lumpur, Kuala Lumpur
5 Department of Pathology, Hospital Raja Permaisuri Bainun, 30450 Ipoh, Perak, Malaysia
6 Department of Pathology, Sarawak General Hospital, 93586 Kuching, Sarawak, Malaysia
7 Subang Jaya Medical Centre, 47500 Subang Jaya, Selangor, Malaysia

Correspondence Address:
Suria Hayati Md Pauzi
Department of Pathology, Faculty of Medicine, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, 56000 Cheras, Kuala Lumpur
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_983_20

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Background: Human epidermal growth factor receptor 2 (HER2) over-expression in breast cancer is associated with aggressive tumor behavior and predicts response to targeted therapy. Accurate HER2 result is paramount for optimal patient management. However, routine HER2 immunohistochemistry (IHC) testing are subjected to intra- and inter-laboratory variability. Objective: This study aims to determine inter-laboratory variation in HER2 IHC testing through a slide-exchange program between five main reference laboratories. Method: A total of 20 breast carcinoma cases with different known HER2 expression and gene status were selected by the central laboratory in five testing rounds. Three unstained tissue sections from each case were sent to participating laboratories, which immunostained and interpreted the HER2 immunohistochemistry result. One of the stained slides was sent to one designated participating laboratory for evaluation. Results were analyzed by the central laboratory. Results: A complete concordance was achieved in six IHC-positive and six IHC-negative cases, its gene status of which was confirmed by in-situ-hybridization (ISH) study. The discordant results were observed in six equivocal cases, one negative case and one positive case with a concordance rate of 50–88.3%. Interestingly, the negative discordant case actually displays tumor heterogeneity. Good inter-observer agreement was achieved for all participating laboratories (k = 0.713-1.0). Conclusion: Standardization of HER2 testing method is important to achieve optimum inter-laboratory concordance. Discordant results were seen mainly in equivocal cases. Intra-tumoral heterogeneity may impact the final HER2 IHC scoring. The continuous quality evaluation is therefore paramount to achieve reliable HER2 results.

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