How is HER2 FISH testing for breast cancer interpreted?

Updated: Jul 16, 2020
  • Author: Maurie Markman, MD, MS; Chief Editor: Karl S Roth, MD  more...
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Newer methodologies for establishing HER2 status, including reverse transcriptase–polymerase chain reaction (RT-PCR) and chromogenic in situ hybridization (CISH), have not yet been validated. The interpretation for HER2 FISH testing (HER2/CEP17 ratio and gene copy number) is given below:

  • Positive HER2 amplification: FISH ratio is greater than 2.2 or HER2 gene copy is greater than 6.0.

  • Equivocal HER2 amplification: FISH ratio of 1.8-2.2 or HER2 gene copy of 4.0-6.0.

  • Negative HER2 amplification: FISH ratio is less than 1.8 or HER2 gene copy of less than 4.0.

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