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doi: https://doi.org/10.4132/jptm.2019.11.03    [Epub ahead of print]
HER2 Status in Breast Cancer: Changes in Guidelines and Complicating Factors for Interpretation
Soomin Ahn1 , Ji Won Woo1,2 , Kyoungyul Lee3 , So Yeon Park1,2
1Department of Pathology, Seoul National University Bundang Hospital, Seongnam, Korea
2Department of Pathology, Seoul National University College of Medicine, Seoul, Korea
3Department of Pathology, Kangwon National University Hospital, Chuncheon, Korea
Corresponding Author: So Yeon Park ,Email: sypmd@snu.ac.kr
Received: October 9, 2019;  Accepted: November 3, 2019.  Published online: November 6, 2019.
HER2 protein overexpression and/or HER2 gene amplification is found in about 20% of invasive breast cancers. It is a sole predictive marker for treatment benefits from HER2 targeted therapy and thus, HER2 testing is a routine practice for newly diagnosed breast cancer in pathology. Currently, HER2 immunohistochemistry (IHC) is used for a screening test, and in situ hybridization is used as a confirmation test for HER2 IHC equivocal cases. Since the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines on HER2 testing was first released in 2007, it has been updated to provide clear instructions for HER2 testing and accurate determination of HER2 status in breast cancer. During HER2 interpretation, some pitfalls such as intratumoral HER2 heterogeneity and increase in chromosome enumeration probe 17 signals may lead to inaccurate assessment of HER2 status. Mover, HER2 status can be altered after neo-adjuvant chemotherapy or during metastatic progression, due to biologic or methodologic issues. This review addressed to recent updates of ASCO/CAP guidelines and factors complicating in the interpretation of HER2 status in breast cancers.
Key Words: Breast cancer; HER2; ASCO/CAP guidelines; HER2 heterogeneity; CEP17 copy number gain
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