. 2022 Sep 1;5(4):882–888. doi: 10.20517/cdr.2022.29

Table 1.

Reporting results of HER2 testing by immunohistochemistry and the corresponding expanded spectrum of positivity (ASCO/CAP 2021)

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

IHC: Immunohistochemistry; HER2: human epidermal growth factor receptor 2.