However, the use of targeted anti-HER2 treatments has been extended to previously treated patients with HER2-low metastatic BC due to phase 3 results of the conjugated antibody Trastuzumab Deruxtecan (T-DXd) demonstrating a significant treatment effect on progression-free survival (PFS) and overall survival (OS) [7]. This evidence concerns the gene ERBB2 and breast cancer.