High inter-laboratory variability in the assessment of HER2-low breast cancer: a national registry study on 50,714 Danish patients

Table 1 Immunohistochemical scoring of HER2 as recommended by American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) in the guidelines first released in January 2007* and revised in November 2013† and November 2018‡

HER2 score	HER2 status	ASCO/CAP guidelines 2007*	ASCO/CAP guidelines 2013^†	ASCO/CAP guidelines 2018^‡
0	Negative	No staining	No staining or faint, incomplete membrane staining in ≤ 10% of tumor cells	No staining or faint, incomplete membrane staining in ≤ 10% of tumor cells
1+	Negative	Weak, incomplete membrane staining in any proportion of tumor cells	Faint, incomplete membrane staining in > 10% of tumor cells	Faint, incomplete membrane staining in > 10% of tumor cells
2+	Equivocal, dependent on supplementary in situ hybridization	Nonuniform or weak, complete, circumferential membrane staining in ≥ 10% of tumor cells or intense, complete membrane staining in ≤ 30% of tumor cells	Incomplete and/or weak to moderate, circumferential membrane staining in > 10% of tumor cells or intense, complete, circumferential membrane staining in ≤ 10% of tumor cells	Weak to moderate, complete membrane staining in > 10% of tumor cells or intense, complete membrane staining in ≤ 10% of tumor cells
3+	Positive	Uniform intense membrane staining in > 30% of tumor cells	Intense, complete, circumferential membrane staining in > 10% of tumor cells	Intense, complete, circumferential membrane staining in > 10% of tumor cells

*Wolff AC, Hammond ME, Schwartz JN, et al. American Society of Clinical Oncology/College of American Pathologists guideline recommendations for human epidermal growth factor receptor 2 testing in breast cancer. J Clin Oncol. 2007;25(1):118–145
^†Wolff AC, Hammond ME, Hicks DG, et al. Recommendations for human epidermal growth factor receptor 2 testing in breast cancer: American Society of Clinical Oncology/College of American Pathologists clinical practice guideline update. J Clin Oncol. 2013;31(31):3997–4013
^‡Wolff AC, Hammond MEH, Allison KH, et al. Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: American Society of Clinical Oncology/College of American Pathologists Clinical Practice Guideline Focused Update. J Clin Oncol. 2018;36(20):2105–2122

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