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. 2022 Sep 1;5(4):882–888. doi: 10.20517/cdr.2022.29

Table 2.

Reporting results of HER2 testing by in situ hybridization (ASCO/CAP 2021)

Result Assay Criteria
Positive
 Single probe CN ≥ 6.0
CN ≥ 4.0 and CN < 6.0 and IHC = 3+
CN ≥ 4.0 and CN < 6.0 and dual ISH ratio ≥ 2.0
Dual probe Ratio ≥ 2.0 and CN ≥ 4.0
Ratio ≥ 2.0 and CN < 4.0 and IHC = 3+
Ratio < 2.0 and CN ≥ 6.0 and IHC > 1+
Ratio < 2.0 and 4.0 ≤ CN > 6.0 and IHC = 3+
Negative
 Single probe CN < 4.0
CN ≥ 4.0 and CN < 6.0 and IHC < 3+
CN ≥ 4.0 and CN < 6.0 and dual ISH ratio < 2.0 and CN < 4.0
Dual probe Ratio ≥ 2.0 and CN < 4.0 and IHC < 3+
Ratio < 2.0 and CN ≥ 6.0 and IHC < 2+
Ratio < 2.0 and 4.0 ≤ CN > 6.0 and IHC < 3+
Ratio < 2.0 and CN < 4.0

CN: Average HER2 copy number (signals/cell); IHC: immunohistochemical score; ratio: HER2/CEP17 ratio.