Novel HER2-targeted ADCs including trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd, also known as DS-8201) are implemented in the treatment of HER2-positive breast cancer, such as in the EMILIA and DESTINY-Breast03 studies [16,17], and explored in treating BCBM [18,19]. This evidence concerns the gene ERBB2 and breast cancer.