Breast Cancer With a HER2 IHC2+ and FISH HER2/CEP17 Ratio ≥2.0 and an Average HER2 Gene Copy Number

Yuanyuan Liu,Xuan Zeng,Xiaohua Shi,Feng Mao,Shafei Wu

doi:10.3389/fonc.2020.00985

Abstract

Purpose: For breast cancer, accurately illustrating HER2 characteristics is a critical precondition for evaluating the prognosis and predicting the efficacy of anti-HER2 therapy. Our purpose was to expose HER2 mRNA expression through an in situ hybridization assay (RNAscope), to aid the identification of HER2 status in breast cancers with a previously controversial classification for patients suffering from a HER2 IHC2+ and HER2/CEP17 ≥2.0 and a <4.0 mean HER2 gene copy number/cell (entitled FISH group 2 by update 2018 HER2 testing guideline).Methods: A total of 8,983 cases of breast cancer with a known HER2 status detected by initial IHC, and a necessary reflex FISH assay for those with IHC2+, were retrospectively analyzed. Then, 41 cases of HER2 IHC2+ in the FISH group 2 were collected and a RNAscope was performed.Results: The incidence of breast cancers with IHC2+ and in the FISH group 2 was 0.46% (41/8,983) in our single-institutional study cohort. In most of the cases (27/41, 65.9%), low levels of HER2 mRNA expression (score 1 and 2 by RNAscope) were demonstrated. Only one case (1/41, 2.4%) of high-level HER2 mRNA expression (score 4 by RNAscope), harboring a FISH HER2/CEP17 ratio of 2.06 and an average HER2 copy number of 3.70, was revealed. One case with the highest FISH HER2/CEP17 ratio of 3.90, showed the lowest level of HER2 mRNA expression (score 1 by RNAscope). Two cases with the same highest average HER2 signals/cell (3.95) by FISH possessed score 3 and score 2 with RNAscope, respectively. No cases with a score of 0 by RNAscope occurred in our sample. In the majority of cases (35/41, 85.4%), hypodisomy of chromosome 17 (average CEP17 signals/cell ≤1.75) was observed. There was no significant relationship between the mRNA expression and FISH results (average HER2 signals/cell, average CEP17 copy number, or HER2/CEP17 ratio) and clinicopathological features (ER and PR statuses, Ki 67 index, tumor size, and lymph node metastasis) in our population.Conclusion: HER2 mRNA overexpression was not a feature in our group of patients. Based on our data, breast cancers with HER2 IHC2+ and in FISH group 2 support a categorization of HER2 negative.

Highlights

Much data has shown that human epidermal growth factor receptor 2 (HER2) gene amplification and/or protein overexpression occurs in ∼25 to 30% of all breast cancers and closely contributes to a poor prognosis as well as an encouragingly good response to HER2-targeting agents, such as anti-HER2 monoclonal antibodies and antibody–drug conjugates [1,2,3]
In China, the IHC assay, which is of widespread popularity, is used for initial HER2 testing in breast cancer based on automatically staining a platform of Ventana Benchmark with 4B5 primary antibody, followed up by those well-acquainted with the interpretation criteria
Compared to IHC, fluorescence in situ hybridization (FISH) assay [commonly used as dual-probe including the HER2 gene and centromere enumeration probe for chromosome 17 (CEP17)], for inspecting HER2 gene copy numbers and amplification because it is more precise in recognizing a HER2 status based on its available research and clinical evidence, has been widely applied for reflex examination and confirmation of HER2 status in specimens with equivocal HER2 IHC results (IHC2+) [4]

Summary

Introduction

Much data has shown that human epidermal growth factor receptor 2 (HER2) gene amplification and/or protein overexpression occurs in ∼25 to 30% of all breast cancers and closely contributes to a poor prognosis as well as an encouragingly good response to HER2-targeting agents, such as anti-HER2 monoclonal antibodies and antibody–drug conjugates (e.g., trastuzumab, pertuzumab, and trastuzumabemtansine) [1,2,3]. In China, the IHC assay, which is of widespread popularity, is used for initial HER2 testing in breast cancer based on automatically staining a platform of Ventana Benchmark with 4B5 primary antibody, followed up by those well-acquainted with the interpretation criteria. Compared to IHC, FISH assay [commonly used as dual-probe including the HER2 gene and centromere enumeration probe for chromosome 17 (CEP17)], for inspecting HER2 gene copy numbers and amplification because it is more precise in recognizing a HER2 status based on its available research and clinical evidence, has been widely applied for reflex examination and confirmation of HER2 status in specimens with equivocal HER2 IHC results (IHC2+) [4]. HER2 status can be determined through IHC and if necessary, followed by FISH detection and vice versa (initial HER2 detection by FISH followed by IHC for FISH-equivocal cases). For a few cases with uncommon HER2 features and a very low incidence (

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