What is the scoring method for HER2 expression in breast cancer testing?

Updated: Jul 16, 2020
  • Author: Maurie Markman, MD, MS; Chief Editor: Karl S Roth, MD  more...
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Although several methods for HER2 testing have been developed, approximately 20% of current HER2 testing may be inaccurate. Therefore, the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) have recommended guidelines in HER2 testing to ensure accuracy.

Breast cancer specimens should initially undergo HER2 testing by a validated immunohistochemistry (IHC) assay (ie, HercepTest, Dako, Glostrup, Denmark) for HER2 protein expression. [7] The scoring method for HER2 expression is based on the cell membrane staining pattern and is as follows:

  • 3+: Positive HER2 expression - Uniform intense membrane staining of more than 30% of invasive tumor cells.

  • 2+: Equivocal for HER2 protein expression - Complete membrane staining that is either nonuniform or weak in intensity but has circumferential distribution in at least 10% of cells.

  • 0 or 1+: Negative for HER2 protein expression.

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