ERBB2 and breast cancer: HER2 IHC status was distributed as follows: 103 (20.3%) HER2 IHC 0, 256 (50.4%) HER2 IHC 1+, and 149 (29.3%) HER2 IHC 2+/ISH−, with HER2-low breast cancer accounting for 79.7% of cases.