ERBB2 and neoplasm: In mediating its cytotoxic action, trastuzumab is known to bind to the domain IV of the extracellular domain of HER2 and triggers cascade tumor-suppressive actions including the activation of antibody-dependent cell-mediated cytotoxicity, inhibition of HER2 extracellular domain cleavage, disruption of HER2 receptor homo- and heterodimerization extracellular segment of HER2 and consequently resulting in the inhibition of HER2-mediated malignant transformation [1, 2].