HER2 Testing: Past and Present


HER2 gene (aka ERBB2) amplification is directly related to HER2 protein overexpression in human breast carcinomas. This somatically acquired genetic alteration is associated with shorter disease-free and overall survival of patients in the absence of HER2-targeted therapy. Because HER2-targeted therapies have significantly improved outcomes for patients whose cancers have this alteration, accurate assessment of the alteration with companion diagnostics is considered critically important. US Food and Drug Administration (FDA)-approved companion diagnostics assess either HER2 gene amplification using fluorescence in situ hybridization (FISH) or HER2 protein overexpression using immunohistochemistry (IHC) assays. In an effort to standardize evaluations of HER2 status, the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) have convened committees to establish guidelines for assessment of HER2 status. These guidelines were published in 2007, 2013 / 2014, and 2018. Although HER2 IHC assays have challenges, with both false-negative and false-positive results, these assays are easily performed and easily interpreted. Each set of the guidelines consider IHC to be a suitable method for assessment of HER2 status, except in the IHC 2+ category, which is considered “equivocal” with supplementary testing recommended using FISH for definitive assignment to a “HER2-positive” or “HER2-negative” designation. The interpretative approaches to assessment of HER2 gene amplification by FISH recommended by the ASCO-CAP guidelines have changed over the years with current guidelines designating 5 different groups according to HER2 FISH ratio and average HER2 gene copy number per tumor cell. The ASCO-CAP FISH groups are “group 1,” designated in situ hybridization (ISH)–positive, has a HER2-to-chromosome 17 centromere (CEP17) ratio ≥2.0 and an average HER2 gene copy number per tumor cell ≥4.0; FISH “group 2,” formerly (2013) designated as “ISH-positive”, has cancer cells with HER2-to-CEP17 ratio ≥2.0 but an average HER2 gene copy number per tumor cell <4.0; FISH “group 3,” also formerly designated as “ISH-positive”, has cancer cells with HER2-to-CEP17 ratio <2.0 and an average HER2 gene copy number per tumor cell ≥6.0; FISH “group 4”, formerly and currently designated as “ISH-equivocal”, has cancer cells with HER2-to-CEP17 ratio <2.0 and an average HER2 gene copy number per tumor cell ≥4.0 but <6.0; FISH “group 5”, designated as ISH-negative, has cancer cells with HER2-to-CEP17 ratio <2.0 and an average HER2 gene copy number per tumor cell <4.0. At the time when these FISH guidelines were initially published, there were no studies using this interpretative strategy and, therefore, no available data related to prevalence rates of each FISH group, correlation of each FISH group with HER2 protein expression, or correlation of each group with clinical outcomes, either with or without HER2-targeted therapies. Since their publication in 2013 / 2014 we, and others, have assessed these prevalence rates and correlations. These findings, some supporting and some contradicting the guidelines, will be summarized in the presentation.

Originally published on August 30, 2021

Lecture Presenter

Michael F. Press, MD, PhD

Michael F. Press, MD, PhD

Harold E. Lee Chair for Cancer Research, Department of Pathology, Norris Comprehensive Cancer Center, University of Southern California

Dr. Press is a Professor in the Department of Pathology and holds the Harold E. Lee Chair in Cancer Research at the University of Southern California’s Norris Comprehensive Cancer Center. Dr. Press is a board-certified pathologist, directs the USC Breast Cancer Analysis Laboratory as well as the Central Laboratory for the Translational Research In Oncology (TRIO)/Cancer International Research Group (CIRG), and is Leader of the USC Clinical Laboratories.

His laboratory evaluates prognostic and predictive markers used in making treatment decisions for women with breast cancer. It has served as the Central Laboratory for either retrospective or prospective analyses of tissue specimens for more than 20 clinical trials that collectively accrued more than 13,000 patients. Dr. Press’s area of research interest is in molecular alterations of breast and gynecologic cancers, especially those that have the potential to be important in either diagnostic or therapeutic decision-making for patient management. His research has been continuously funded by research grants for more than 30 years. He is the author or co-author of more than 250 peer-reviewed publications. The most prominent area of activity for his laboratory has been in the study of the human epidermal growth factor receptor type 2 (HER2) in breast and other cancers. He published his first paper in this area in 1989 (Science 244: 707-712, 1989) and his laboratory is still actively contributing to this area as well as to the conduct of clinical trials evaluating HER2 as a target for therapy.


After this presentation, participants will be able to:

  • Recognize the importance of HER2 gene amplification/overexpression as a therapeutic target
  • Describe the role of accurate HER2 laboratory testing in the selection of patients for HER2-targeted therapies
  • Discuss the limitations of various HER2 testing methods and understand the impact on patient outcomes

Sponsored by:

University of Utah School of Medicine, Department of Pathology, and ARUP Laboratories