Antibody–drug conjugates (ADCs), which combine a HER2-targeted mAb and a cytotoxic drug, like the FDA-approved compounds trastuzumab emtansine (T-DM1) and fam-trastuzumab deruxtecan (T-DXd) showed significant improvement in progression-free and overall survival compared to standard chemotherapy, thus improving BC patient prognosis [46–49]. This evidence concerns the gene ERBB2 and breast cancer.