Quantitative assessments and clinical outcomes in HER2 equivocal 2018 ASCO/CAP ISH group 4 breast cancer

Swati Gupta,Jodi Weidler,Brian Rhees,David L Rimm,Kenneth Ho,John Mcguire,Michael Bates,Yan S Song,Veronique Neumeister,Wendy Wong,Veerle Bossuyt,Balazs Acs

doi:10.1038/s41523-019-0122-x

Abstract

We quantified human epidermal growth factor receptor 2 (HER2) RNA and protein expression in 2018 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) in situ hybridization (ISH) group 4 (HER2/centromeric probe 17 (CEP17) ratio <2.0, average HER2 copy number ≥4.0 and <6.0, and 2013 ASCO/CAP ISH equivocal) breast cancers. Breast cancers in 2018 ASCO/CAP ISH group 4 between 2014 and 2017 were identified from the Yale archives. Sixty-three patients (34 with HER2 immunohistochemistry (IHC) 0/1+ and 29 with HER2 IHC 2+) were included. We compared patient characteristics, systemic treatments, and outcomes. We assessed HER2 by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and quantitative immunofluorescence (QIF). Among ISH group 4 cancers, higher HER2 mRNA (P < 0.0001) but similar HER2 protein levels were observed in IHC 2+ compared to IHC 0/1+ cancers. The distribution of RT-qPCR and QIF scores were independent of fluorescence in situ hybridization (FISH) ratio/copy number. Concordance between HER2 RT-qPCR and QIF was 69.8% (r = 0.52). Among 29 patients with IHC2+ results, 16 were HER2 positive by RT-qPCR and 12 were HER2 positive by QIF. Systemic treatment, recurrence, and survival outcomes were comparable among ISH group 4 cancers regardless of IHC 0/1+ or 2+ results. ISH group 4 cancers appear to form a distinct group with intermediate levels of RNA/protein expression, close to positive/negative cut points. Therefore, adjudication into positive or negative categories may not be meaningful. Our results support the 2018 ASCO/CAP recommendation to refrain from routine additional testing of these samples. Additional outcome information after trastuzumab treatment for patients in this special group might help to guide treatment decisions in these patients.

Highlights

Breast cancer can be classified into two major clinically important groups by immunohistochemistry (IHC): human epidermal growth factor receptor 2 (HER2) positive (IHC 3+) and HER2 negative (IHC 0/1+)
HER2 fluorescence in situ hybridization (FISH) with alternative chromosome 17 probes has been proposed to reclassify a subset of these cases as positive based on HER2/CHR17 probe ratio.[6,7]
If IHC is 2+, additional ISH testing by an observer blinded to the previous results to recount at least 20 cells is recommended

Summary

Introduction

Breast cancer can be classified into two major clinically important groups by immunohistochemistry (IHC): human epidermal growth factor receptor 2 (HER2) positive (IHC 3+) and HER2 negative (IHC 0/1+). Oncology and the College of American Pathologists (ASCO/CAP) guidelines, equivocal IHC results (IHC 2+) should be reflex in situ hybridization (ISH) tested on either the same or an alternative specimen.[1] Patients with ISH HER2/centromeric probe 17 (CEP17) ratio ≥2.0 or with HER2 copy number >6.0 are eligible for antiHER2 therapy. Reflex testing resolves most cases; a subset remains difficult to classify by ISH when ISH HER2/CEP17 ratio is

Methods

Results

Conclusion