HER2 FISH findings in the breast carcinomas with equivocal (2+) HER2 immunostaining (N=345)
| N | % | |
| HER2 gene copy number | ||
| Non-amplified (HER2/CEP17 ratio <1.8) | 281 | 81.4 |
| Equivocal (HER2/CEP17 ratio 1.8–2.2) | 34 | 9.9 |
| HER2 amplified (HER2/CEP17 ratio >2.2) | 30 | 8.7 |
| Low-grade amplification (HER2/CEP17 ratio >2.2–<4) | 17 | 4.9 |
| High-grade amplification (HER2/CEP17 ratio ≥4) | 13 | 3.8 |
| HER2 genetic heterogeneity | ||
| Present | 137 | 39.7 |
| Absent | 208 | 60.3 |
| HER2 gene cluster | ||
| Present | 20 | 5.8 |
| Absent | 325 | 94.2 |
| Chromosome 17 copy number | ||
| Hypodisomy 17 (chromosome 17 copy number <1.5) | 7 | 2.0 |
| Disomy 17 (chromosome 17 copy number 1.5–2.25) | 269 | 78.0 |
| Polysomy 17 (chromosome 17 copy number >2.25) | 69 | 20.0 |
| Low polysomy 17 (chromosome 17 copy number >2.25 but ≤3.75) | 69 | 20.0 |
| High polysomy 17 (chromosome 17 copy number >3.75) | 0 | 0 |
CEP17, 17 centromeric probe; FISH, fluorescence in-situ hybridisation.