**6.5 EGFR**

Epidermal growth factor receptor (EGFR) is a family of transmembrane growth factor receptor tyrosine kinases involved in regulation of cell proliferation and survival of epithelial cells (Cleator & Heller, 2007). EGFR family includes four receptors: EGFR/ErbB1, HER2/ErbB2, HER3/ErbB3 and HER4/ErbB4. EGFR and HER2 are over expressed in approximately 40% and 25% of breast cancers, respectively and associated with aggressive clinical behavior and poor prognosis. Due to the important roles of EGFR and HER2 receptors in diagnosis and therapy of breast cancer patients, both receptors are discussed in details (Munagalaet al., 2011).

#### • **EGFR receptor**

EGFR (also known as ErbB1 or HER1) is a 170 kDa transmembrane protein with an intracellular tyrosine-kinase domain. Many epithelial cancers including tumors of the head and neck, breast, colon, lung, kidney, prostate, brain, bladder and pancreas overexpress EGFR. Such overexpression is associated with poor prognosis and this leads to several strategies to block this pathway and improve the outcome. Cetuximab is a chimeric IgG1 monoclonal antibody that competes with an endogenous ligand to bind to the extracellular domain of EGFR (Harris, 2004). On the basis of these findings and those of previous studies, Cetuximab received FDA approval in February 2004, for using in treatment of EGFRpositive metastatic colorectal cancer (Harris, 2004).
