ERBB2 and breast carcinoma: Recent literature has introduced more granular categories for HER2-negative breast cancer: HER2-low (IHC 1+ or IHC 2+/ISH−), HER2-ultralow (IHC 0 with membrane staining), and HER2 IHC 0 absent membrane staining (Figure 1) [5,6,7,8].