Trastuzumab (Herceptin®) is a humanized IgG1mAb that binds to the extracellular domain of HER2, a tyrosine kinase receptor that is upregulated in 20% of breast cancer (BC) patients, preventing its homodimerization and thereby blocking its intracellular signaling (Greenblatt and Khaddour, 2023). Here, ERBB2 is linked to breast cancer.