Table 1.

Consensus Panel Recommendations on HER2/neu Immunohistochemistry Scoring for Gastroesophageal Adenocarcinoma Biopsy and Resection Specimens^a

Reactivity Characteristics	Score/Classification
Resection specimens
No reactivity (at ×40 magnification)	0/negative
Membranous reactivity in <10% of cells
Faint/barely perceptible partial membranous reactivity in >10% of tumor cells (at ×40 magnification)	1+/negative
Weak/moderate complete OR basolateral/lateral membranous reactivity in >10% of tumor cells (at ×10–×20 magnification)	2+/equivocal
Moderate/strong complete OR basolateral/lateral membranous reactivity in >10% of tumor cells	3+/positive
Unequivocal membranous staining at low magnification (×2.5/×5)
Biopsy specimens
Any single cluster of tumor cells (≥5 cells) demonstrating IHC 3+ staining characteristics	3+/positive

Abbreviation: HER2/neu, human epidermal growth factor receptor 2; IHC, immunohistochemistry.

^aAdapted from Hoffman et al¹³ and Rüschoff et al.²⁵ Reprinted with permission.