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Analytic Guidelines: Interpretation

Interpretation criteria for all types of HER2 tests must be standardized and refined, based on the interpretation criteria from recent clinical trials and international experience. Reporting elements for HER2 testing must also be standardized. In laboratories with multiple pathologists, it may also be advisable to consider limiting the number who interpret HER2 tests, so that each pathologist will interpret a greater number of cases.
When HER2IHC is performed first:
  • If 0 or 1+, result is negative - stop testing. If the specimen is an excision in which HER2 was previously performed on the initial biopsy and was negative for HER2, and it meets any of the following criteria, it is recommended that the HER2 be repeated:
    • Tumor is grade 3
    • Amount of invasive tumor in the core biopsy is small
    • Resection of specimen contains high grade carcinoma that is morphologically distinct form that in the core
    • Core biopsy results in equivocal for HER2 after testing by both IHC and ISH
    • There is doubt that the specimen handling was adequate on the core biopsy (eg, long ischemic time, short time in fixative, different fixative used, or test is suspected by the pathologist to be negative on the basis of testing error)
  • If 2+, result is equivocal - reflex to HER2 FISH
  • If 3+, result is positive - stop testing. If the specimen is an excision in which HER2 was previously performed on the initial biopsy and was positive in grade 1 carcinoma, it is recommended that the HER2 be repeated.