Interpretation criteria for all 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, limiting the number of pathologists who interpret HER2 tests may also be advisable so that each pathologist will interpret more cases.
When HER2 IHC is performed first:
- If 0 or 1+, the 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. If 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 a morphologically distinct form in the core
- There is doubt that the specimen handling was adequate on the core biopsy (e.g., long ischemic time, short time in fixative, different fixative used, or test is suspected by the pathologist to be negative based on testing error)
- If 2+, the result is equivocal—must reflex to HER2 FISH.
- If 3+, the result is positive—stop testing. If the specimen is an excision in which HER2 was previously performed on the initial biopsy and was positive for grade 1 carcinoma, it is recommended that the HER2 be repeated.
