Table 1.

Immunohistochemical scoring systems and ISH definitions of HER2 evaluation across the different tumor types analyzed.

Type of Tumor	Recommended HER2 IHC Scoring Systems	Interpretation of HER2 IHC	Interpretation of ISH
Salivary gland carcinoma	Breast cancer criteria with Hercept test: score 0: no staining observed or Incomplete membrane staining that is faint or barely perceptible and within ≤10% of the invasive tumor cells score 1+: Incomplete membrane staining that is faint or barely perceptible and within >10% of the invasive tumor cells score 2+: Weak to moderate complete membrane staining observed in >10% of tumor cells score 3+: Circumferential membrane staining that is complete, intense, and in >10% of tumor cells	Score 0 and 1+: negative Score 2+: equivocal, need ISH confirmation Score 3+: positive	Breast cancer criteria: ISH negative: -HER2/CEP17 ratio < 2.0 with an average HER2 copy number < 4.0 (group 5); -HER2/CEP17 ratio ≥ 2.0 and average HER2 copy number < 4.0 (group 2) with concurrent IHC 2+; -HER2/CEP17 ratio < 2.0 with an average HER2 copy number ≥ 4.0 and < 6.0 (group 4) with concurrent IHC 2+; -Groups 2, 3, and 4 with concurrent IHC 0 or 1+. ISH positive: -HER2/CEP17 ratio ≥ 2.0 and average HER2 copy number ≥ 4.0 (group 1); -HER2/CEP17 ratio ≥ 2.0 and average HER2 copy number < 4.0 (group 2) with concurrent IHC 3+; -HER2/CEP17 ratio < 2.0 and average HER2 copy number ≥ 6.0 (group 3) with concurrent IHC 2+; -HER2/CEP17 ratio < 2.0 and average HER2 copy number ≥ 6.0 (group 3) with concurrent IHC 3+; -HER2/CEP17 ratio < 2.0 with an average HER2 copy number ≥ 4.0 and < 6.0 (group 4) with concurrent IHC 3+.
HNSCC	See salivary gland carcinoma	See salivary gland carcinoma	See salivary gland carcinoma
Lung cancer	See salivary gland carcinoma	See salivary gland carcinoma	See salivary gland carcinoma
Biliary tract cancer	Gastroesophageal cancer criteria with Hercept test: Score 0: No reactivity or membranous reactivity in <10% of tumor cells Score 1+: Faint or barely perceptible membranous reactivity in ≥10% of tumor cells; cells are reactive only in part of their membrane. Score 2+: Weak to moderate complete, basolateral or lateral membranous reactivity ≥ 10% of tumor cells Score 3+: strong complete, basolateral or lateral membranous staining in ≥10% of tumor cells	Score 0 and 1+: negative Score 2+: equivocal, ISH confirmation is needed Score 3+: positive	Gastroesophageal cancer criteria: ISH positive: -HER2: centromeric probe for chromosome 17 (CEP17) ratio of ≥2)
Colorectal cancer	CAP/ASCP/ASCO GEA: Score 0: no reactivity or membranous reactivity in <10% Score 1+: faint/barely perceptible reactivity in ≥10% Score 2+: weak to moderate complete, basolateral, or lateral membranous reactivity in ≥10% but <50% Score 2+: weal to moderate complete, basolateral, or lateral membranous reactivity in ≥50% Score 3+: strong complete, basolateral, or lateral membrane staining in 10–50% Score 3+: strong complete, basolateral, or lateral membrane staining > 50% HERACLES Diagnostic Criteria with Ventana 4B5: Score 0: no staining Score 1+: faint staining, any cellularity, segmental or granular pattern Negative (2+): moderate staining in <50% cells, any pattern Equivocal (2+): moderate staining in ≥50% cells, any pattern with circumferential, basolateral or lateral pattern (IHC mandatory: re-test IHC; if confirmed, proceed with ISH) Negative (3+): intense in ≤10% cells, circumferential, basolateral or lateral pattern Positive (3+): intense in >10% and <50% cells, circumferential, basolateral or lateral pattern (IHC mandatory: re-test IHC; if confirmed, proceed with ISH) Positive (3+): intense in ≥50% cells, circumferential, basolateral, or lateral pattern	CAP/ASCP/ASCO GEA: Score 0 and 1+: negative Score 2+: equivocal, need ISH confirmation HERACLES Diagnostic Criteria with Ventana 4B5: Score 0 and 1+: negative Negative (2+): moderate staining in <50% cells, any pattern Equivocal (2+): moderate staining in ≥50% cells, any pattern with circumferential, basolateral or lateral pattern (IHC mandatory: re-test IHC; if confirmed, proceed with ISH) Negative (3+): intense in ≤10% cells, circumferential, basolateral or lateral pattern Positive (3+): intense in >10% and < 50% cells, circumferential, basolateral or lateral pattern (IHC mandatory: re-test IHC; if confirmed, proceed with ISH) Positive (3+): intense in ≥50% cells, circumferential, basolateral or lateral pattern	CAP/ASCP/ASCO GEA and HERACLES Diagnostic Criteria: -HER2/CEP17 ratio ≥ 2 in ≥50% of cells
Urothelial cancer	See salivary gland carcinoma and biliary tract cancer	See salivary gland carcinoma and biliary tract cancer	See salivary gland carcinoma and biliary tract cancer
Prostate cancer	See salivary gland carcinoma	See salivary gland carcinoma	See salivary gland carcinoma
Gynecological cancer	Score 2+: intense complete or basolateral/lateral membrane staining in 30% or fewer tumor cells or weak to moderate staining in greater than or equal to 10% of tumor cells Score 3+: Intense complete or basolateral/lateral membrane staining in over 30% of tumor cells	Score 2+: equivocal, must order reflex test (same specimen using ISH) or order a new test (new specimen if available, using IHC or ISH). Score 3+: positive	ISH negative: -FISH HER2/CEP17 ratio < 2.0 and average HER2 copy number less than 6 per nucleus ISH positive: -FISH HER2/CEP17 ratio ≥ 2.0; -FISH HER2/CEP17 ratio < 2.0 with average HER2 copy number equal to or greater than 6 per nucleus.
Thyroid cancer	See salivary gland carcinoma	See salivary gland carcinoma	See salivary gland carcinoma
RCC	See salivary gland carcinoma	See salivary gland carcinoma	See salivary gland carcinoma
PDAC	See biliary tract cancer	See biliary tract cancer	See biliary tract cancer
HCC	See biliary tract cancer	See biliary tract cancer	See biliary tract cancer
Small bowel adenocarcinoma	See biliary tract cancer	See biliary tract cancer	See biliary tract cancer
Anal cancer	See biliary tract cancer	See biliary tract cancer	See biliary tract cancer
Non-melanoma skin cancers	NR	NR	NR

Abbreviations: CEP17, chromosome enumeration probe 17; HER2, human epidermal growth factor receptor 2; HNSCC, head and neck squamous cell carcinoma; IHC, immunohistochemical; ISH, in situ hybridization; NR: not reported in the literature; PDAC, pancreatic ductal adenocarcinoma; RCC, renal cell carcinoma.