- HER2 must be reported POSITIVE with ISH based on:
- Single-probe, average HER2 copy number ≥ 6.0 signals/cell
- Dual-probe HER2/CEP17 ratio ≥ 2.0 with an average HER2 copy number ≥ 4.0 signals/cell
- Dual-probe HER2/CEP17 ratio ≥ 2.0 with an average HER2 copy number <4.0 signals/cell
- Dual-probe HER2/CEP17 ratio < 2.0 with an average HER2 copy number ≥ 6.0 signals/cell
- HER2 must be reported as EQUIVOCAL with ISH based on:
- Single-probe ISH average copy number ≥ 4.0 and < 6.0 signals/cell
- Dual-probe HER2/CEP17 ratio < 2.0 with an average HER2 copy number ≥ 4.0 and < 6.0 signals/cell
- HER2 must be reported as NEGATIVE with ISH based on:
- Single-probe average HER2 copy number < 4.0 signals/cell
- Dual-probe HER2/CEP17 ratio < 2.0 with an average HER2 copy number < 4.0 signals/cell
Counting is performed on at least 20 cells. A pathologist must confirm the counting and involves only the invasive component. Comparisons are needed to distinguish between normal breast and tumor cells in order to manage interpretation of difficult to interpret areas. CISH amplification is defined as >10 discrete copies per nucleus or as large gene copy clusters in >50% of nuclei. Unaltered gene copy is 1-5 copies per nucleus (Tanner).