Epidermal growth factor receptor (EGFR) is a 170 kDa transmembrane glycoprotein receptor tyrosine kinase that, when activated by epidermal growth factor (EGF), affects cell growth and differentiation in normal and cancer cells. Binding of EGF or TGF alpha to EGFR activates tyrosine kinase activity of the receptor. The carboxy-terminal tyrosine residues on EGFR, Tyr 1068, Tyr 1148, and Tyr 1173, are the major sites of autophosphorylation, which occurs as a result of EGF binding. EGFR overexpression is exhibited in various cancers, such as glioma, colorectal carcinoma, breast carcinoma, and head and neck carcinoma. The phosphorylation level of EGFR is considered to be one of the most important predictors for the clinical outcome of non-small cell lung and breast cancer.