Table 4. Interpretation of IHC findings [244,245].
HER2 status | Intensity | IHC staining |
---|---|---|
Negative | 0 | Reactivity in <10%* of tumor cells |
Negative | 1+ | Faint membranous† reactivity in ≥10% of tumor cells; reactive only in part of their membrane |
Equivocal | 2+ | Weak to moderate complete or basolateral membranous reactivity in ≥10% of tumor cells |
Positive | 3+ | Strong complete or basolateral membranous reactivity in ≥10% of tumor cells |
IHC = immunohistochemistry; HER2 = human epidermal growth factor receptor 2.
*For biopsy samples, measure scores when stained tumor cell clusters (≥5 cells) are present, irrespective of the percentage of tumor cells; †Only membranous staining should be considered true reactivity.