The FDA-Approved Breast Cancer HER2 Evaluation kit (HercepTest; Dako) May Miss Some HER2-Positive Breast Cancers

Frank Schneider, MD; Yulan Jin, MD, PhD; Kevin Van Smaalen, MD; Evin H. Gulbahce, MD; Rachel E. Factor, MD; Xiaoxian Li, MD, PhD

Disclosures

Am J Clin Pathol. 2019;151(5):504-510. 

In This Article

Abstract and Introduction

Abstract

Objectives: Accurate evaluation of human epidermal growth factor receptor 2 (HER2) in breast cancer is critical.

Methods: HER2 fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) tests were performed on 52 cases using a US Food and Drug Administration (FDA)–approved kit (HercepTest, FDA kit) and a laboratory-developed test (LDT) with the HercepTest antibody and a Leica Bond automated stainer.

Results: By FISH, 22 were HER2 positive, 29 were negative, and one was equivocal. Of the 22 HER2 FISH-positive cases, five were negative by the FDA kit and none by LDT. The five discrepant cases were retested using the same FDA kit in another Clinical Laboratory Improvement Amendments–certified laboratory, and all five cases were still negative. None of the 29 HER2 FISH-negative cases were positive by the FDA kit or LDT. The overall IHC-FISH concordance rate was 90.4% for the FDA kit and 100% for the LDT.

Conclusions: The FDA kit may miss some HER2-positive cases. The LDT has a higher sensitivity and a higher concordance rate with FISH results.

Introduction

Human epidermal growth factor receptor 2 gene (HER2, also referred as ERBB2) is an oncogene encoding a transmembrane tyrosine kinase receptor and plays an important role in the tumorigenesis of HER2-positive (HER2+) breast cancer and other cancers.[1] HER2 gene amplification is observed in approximately 15% to 20% of breast cancers.[2–4] HER2-targeted agents, such as trastuzumab and pertuzumab, have significant clinical benefits to patients with HER2+ breast cancer but are ineffective in HER2-negative patients.[5–9] Therefore, accurate determination of HER2 status is critical to select patients for appropriate therapy and to preclude patients from ineffective treatment to avoid side effects and unnecessary economic burdens.

While there are many available methods to assess the HER2 status, immunohistochemistry (IHC) and in situ hybridization (ISH) methods are currently approved and most commonly used in clinical practice.[10,11] Due to the inherent differences between the two methods and variations of preanalytic, analytic, and postanalytic factors, there is considerable intra- and interlaboratory variability.[12–15]To minimize the variability and improve the accuracy of HER2 tests, the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines were initiated in 2007 and then updated in 2013 and 2018.[10,11,16] One of the major goals of the 2013 update was to lower the false-negative rate to maximize the identification of patients with HER2+ breast cancer who may benefit from the HER2-targeted therapy. The 2013 ASCO/CAP guidelines lowered the threshold for HER2 positivity for both IHC (from 30% to 10%) and ISH (HER2/chromosome 17 [CEP17] ratio from ≥2.2 to ≥2.0). The impact of the updated 2013 ASCO/CAP guidelines on clinical practice has been studied extensively.[17–27] Most studies agreed that the 2013 update increased HER2-equivocal cases (reclassified from negative group), which subsequently led to increased fluorescence in situ hybridization (FISH) testing. However, it is unclear whether the 2013 guidelines significantly contribute to detection of additional HER2+ cases for targeted therapy.[17–19,21–23,25]

The ASCO/CAP guidelines include limited guidance on choice of reagents, which may be one major source for interlaboratory discordance. In this validation study, we performed HER2 IHC tests on breast cancer specimens from 52 patients using a US Food and Drug Administration (FDA)–approved kit (HercepTest; Dako) and our laboratory developed test (LDT). We compared the IHC results from both tests with the results from FISH to evaluate the accuracy and concordance of both IHC tests.

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