Assessment of HER2 testing patterns, HER2+ disease, and the utilization of HER2-directed therapy in early breast cancer

Abstract

Context

Determining human epidermal growth factor receptor 2 (HER2) status is critical for the management of early-stage breast cancer (ESBC). An understanding of HER2 testing practices can provide insight into how test results influence the use of HER2-directed therapy.

Objective

To assess HER2 testing, HER2+ disease, and HER2-directed therapy in ESBC at the Huntsman Cancer Institute before and after the 2007 American Society of Clinical Oncology and College of American Pathologist (ASCO/CAP) guidelines on HER2 testing were published.

Methods

Patients were identified from an institutional tumor registry. HER2 testing patterns and results were examined using a chart review of pathology and clinical notes. Patient characteristics, HER2+ rate, and trastuzumab use were evaluated descriptively. Discordance rate with reflex testing (immunohistochemistry [IHC]2+ retested by fluorescence in situ hybridization [FISH]) was also evaluated.

Results

A total of 1,459 women were included (mean age: 57 years). The rate of HER2+ disease was 17% (number [N] =245). The discordance rate between IHC2+ and FISH was 10%. After the 2007 ASCO/CAP guidelines, fewer tumors were classified as IHC3+ (16% post- versus 21.9% pre-2007), more tumors were characterized as IHC2+ (26.4% post- versus 20.7% pre-2007), and the overall HER2+ rate was decreased (18.7% versus 21.9%), but this was not statistically significant (P=0.519). Most patients with HER2+ ESBC received HER2-targeted therapy (N=185).

Conclusion

The HER2+ rate was 17% and within the range of the reported rates in the literature. Reflex testing identified additional HER2+ tumors by approximately 10%, and should be considered a potential quality indicator. ASCO/CAP HER2 testing guidelines in 2007 appeared to impact the interpretation and classification of HER2+ tumors.

Keywords:

• human epidermal growth factor receptor 2
• HER2
• early-stage breast cancer
• immunohistochemistry
• FISH
• HER2-targeted therapy

Acknowledgments

The authors would like to acknowledge Reed Barney and Brian Oberg from the University of Utah Enterprise Data Warehouse for data extraction and management.

Disclosure

This work was supported by an unrestricted research grant by Genentech, Inc. The authors report no other conflicts of interest in this work.

A portion of this work was presented at ASCO’s Quality Care Symposium, November 1–2, 2013, Manchester Grand Hyatt, San Diego, CA, USA.