Additionally, HER2-low status, defined as HER2 FISH-negative cases with HER2 IHC 1+ or 2+ scores, has gained much interest lately due to the availability of new antibody–drug conjugates, such as trastuzumab–deruxtecan (T-Dx), which have been approved for previously treated metastatic BC [83,84]. This evidence concerns the gene ERBB2 and breast cancer.