Accuracy of human epidermal growth factor receptor 2 (HER2) immunohistochemistry scoring by pathologists in breast cancer, including the HER2-low cutoff

Table 1 Central pathologist agreement across HER2 IHC scores for breast cancer samples, used to establish consensus

HER2 IHC score	Three pathologists agree, n (%^a)	Two pathologists agree, n (%^a)	No pathologists agree, n (%^a)
0	78 (15.6)	27 (5.4)	6 (1.2)^{b, c}
1+	90 (18.0)	86 (17.2)
2+	65 (13.0)	43 (8.6)
3+	41 (8.2)	54 (10.8)
Evaluable results	274 (54.8)^b	210 (42.0)^b
Non-evaluable results	7 (1.4)^b	3 (0.6)^b

HER2: human epidermal growth factor receptor 2; IHC: immunohistochemistry
^a Percentage is calculated based on all samples (N = 500)
^b Bolded data encompass all 500 samples
^c Samples with no agreement cannot be categorized according to IHC score or evaluable/non-evaluable results; therefore, data are shown spanning all possible scores

ISSN: 1746-1596