| Score to report | HER2 protein assessment | Staining pattern |
| 0 | Negative | No staining is seen or membrane staining is <10% of invasive tumour cells |
| 1+ | Negative | Faint/barely perceptive membrane staining detected in >10% of invasive tumour cells |
| 2+ | Equivocal | Weak to moderate complete membrane staining in >10% of invasive tumour cells or <30% with strong complete membrane staining |
| 3+ | Positive | Strong complete membrane staining in >30% of invasive tumour cells |
2+ cases should be assessed by FISH, as should other cases where there is heterogeneity, problems with immunohistochemistry interpretation and problems relating to fixation.