Table 1.

Comparison between HER2 score 1+ definition based on the existing guidelines against the refined criteria

Refined definition	Existing ASCO/CAP and UK guidelines
*Faint complete and/or faint incomplete in ≥ 20%	Incomplete membrane staining that is faint/barely perceptible and in > 10% of tumour cells
Weak complete ≤ 10%
Weak incomplete > 10%
Moderate incomplete < 10%

ASCO/CAP, American Society of Clinical Oncology /College of American Pathologists; HER2, human epidermal growth factor receptor 2.

^*Total faint staining in tumour cells ≥ 20%.