ERBB2 and breast cancer: But the remaining 85% of breast cancers patients with HER2-low expression (immunohistochemistry (IHC) 1+ or IHC 2+, fluorescence in situ hybridization (FISH) non-amplified) or HER2-negative expression (IHC 0) failed to derive no benefit from the currently available anti-HER2 treatments (6, 7).