Stepwise approach for the proposed standardised HER2 IHC evaluation protocol
| Step 1 | Evaluate the whole slide at ×10 to identify IHC staining heterogeneity |
| Step 2 | Estimate the percentage of areas with different percentage of HER2 IHC staining (with >10% difference) |
| Step 3 | Evaluate each area at high power field (×40x) and estimate the % of incomplete and complete membranous staining using the eyeballing method |
| Step 4 | Calculate the global HER2 complete and incomplete membranous staining:((average % of positive cell in area 1×% of area 1)+(average % of positive cells in area 2x% of area 2)+(average % of positive cells in area 3x% of area 3) +…+ (average % of positive cells in area N×% of area N))x100 (%) |
IHC, immunohistochemistry.