TABLE 1.

HER2 scoring by immunohistochemistry according to the expanded spectrum of positivity (ASCO/CAP 2021).

Membrane staining pattern	Tumor cells	Score	Classical category	Expanded spectrum
Intense, complete	>10%	3+	HER2+	HER2+
Weak-to-moderate, complete	>10%	2+	HER2+ (if ISH+)	HER2+ (if ISH+)
			HER2- (if ISH-)	HER2-low (if ISH-)
Faint/barely perceptible, incomplete	>10%	1+	HER2-	HER2-low
Faint/barely perceptible, incomplete	≤10%	0	HER2-	HER2 Ultra low
No staining			HER2-	HER2-zero

Abbreviations: IHC, immunohistochemistry; ISH, in situ hybridization; HER2, human epidermal growth factor receptor 2.