 Panitumumab Vectibix is a fully humanized monoclonal antibody directed against epidermal growth factor receptor EGFr, which is a 170-kD transmembrane glycoprotein with a cytoplasmic protein kinase domain essential for tumor growth and division. The receptor binds multiple ligands including epidermal growth factor and transforming growth factor-alpha TGF-alpha. The tyrosine kinase intracellular domain of the receptor is activated via binding of a ligand to EGFr, which in turn initiates a cascade of intracellular signals. These downstream signaling pathways again include the phosphorylation of mitogen-activated protein kinase MAPK through the rasraf pathway. Inhibition of these signaling pathways can result in cell growth arrest and apoptosis, respectively11. 