What is the role of IHC in HER2 breast cancer testing?

Updated: Jul 16, 2020
  • Author: Maurie Markman, MD, MS; Chief Editor: Karl S Roth, MD  more...
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Testing for HER2 may be done by means of either immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH).

The scoring method for HER2 expression on IHC 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.

  • HER2 test results must be reported as indeterminate if technical issues prevent one or both tests from being interpreted accurately.

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