|0 and 1+||Negative |
|2+||Indeterminate requiring FISH for determination of amplification|
|3+||Positive for overexpression/amplification|
An IHC equivocal result (2+) is circumferential membrane staining that is incomplete and/or weak/moderate and within >10% of the invasive tumor cells or complete and circumferential membrane staining that is intense and within less than or equal to 10% of the invasive tumor cells. Some but not all of these samples may have HER2 gene amplification. An equivocal 2+ result requires additional testing to define the true HER2 status.
An IHC result of 3+ cell surface expression (defined as circumferential membrane staining that is complete, intense) is considered positive.