Identification of HER2 Immunohistochemistry-Negative, FISH-Amplified Breast Cancers and Their Response to Anti-HER2 Neoadjuvant Chemotherapy

I-sanna Gibbons-Fideler, MD; Hiroaki Nitta, PhD; Adrian Murillo, PhD; Gary Tozbikian, MD; Peter Banks, MD; Anil V. Parwani, MD, PhD; Zaibo Li, MD, PhD

Disclosures

Am J Clin Pathol. 2019;151(2):176-184. 

In This Article

Abstract and Introduction

Abstract

Objectives: Either immunohistochemistry (IHC) or in situ hybridization (ISH) can be used to determine human epidermal growth factor receptor 2 (HER2) status. Breast cancers (BCs) with HER2 IHC-negative (IHC–) and ISH-amplified (ISH+) results have been rarely reported but not well studied. We investigated the frequency of HER2 IHC–/ISH+ BCs and their response to anti-HER2 neoadjuvant chemotherapy (NAC).

Methods: Seventeen BCs with HER2 IHC–/ISH+ results were identified from 1,107 consecutive invasive BCs (1.5%, 17/1,107).

Results: Gene protein assay confirmed the original HER2 IHC and ISH results. Increased HER2 RNA level was detected in HER2 IHC–/ISH+ cases compared with HER2 IHC–/ISH– cases. Eight patients had anti-HER2 NAC; three had pathologic complete response, and five had residual tumors.

Conclusions: A small percentage of patients (1.5%) showed discordant HER2 IHC and ISH results (IHC–/ISH+) and would have lost the opportunity for potentially beneficial anti–HER2-targeted therapy if only HER2 IHC testing had been used.

Introduction

Human epidermal growth factor receptor 2 (HER2; ERBB2) gene amplification and/or protein overexpression occur in approximately 15% to 20% of invasive breast carcinomas (BCs).[1–3] Accurate determination of HER2 status in patients with breast cancer is critical. False-positive results expose patients to unnecessary therapy with potential side effects, while false-negative results exclude patients from potentially highly effective targeted therapy.[4–6]

Either immunohistochemistry (IHC) for protein expression or fluorescent in situ hybridization (FISH) for gene amplification can be used to determine HER2 status in BC. Both methods are approved by the US Food and Drug Administration (FDA). Each method has its own advantages and disadvantages. FISH is usually used as a reflex test on IHC-equivocal (2+) cases. The 2013 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) HER2 testing guideline has increased the number of HER2 double-equivocal cases (HER2 IHC 2+and HER2 FISH equivocal).[7–9] In addition, the 2013 guidelines have resulted in increasing discordance between IHC and FISH results.[7,8] A recent study has demonstrated that nine of 368 breast cancer cases showed discordant results between IHC and FISH, including eight (2.2%) with IHC-negative/FISH-positive results and one with IHC-positive/FISH-negative results.[10] However, the clinical outcomes, especially response to anti–HER2-targeted therapy, have not been evaluated in such cases.

In our institution, both IHC and FISH are simultaneously performed for initial assessment of core biopsy specimens of invasive BCs. In this study, the purpose was to investigate the frequency of HER2 IHC–/FISH+ invasive BCs and their response to anti-HER2 neoadjuvant chemotherapy (NAC).

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