ERBB2 and breast cancer: BC patients with HER2 IHC score of 3+ achieved pCR in 54% of cases, compared to 19% of those with IHC score of 2+ with FISH amplification (HER2/CEP17 ratio ≥2.0 or HER2 gene copy number ≥6.0 (combined Groups 1, 2 + 3) (p < 0.0001) (Supplementary Table 1).