EGFR (Epidermal growth factor receptor, ErbB-1) is a receptor tyrosine kinase (RTK) that is one of four members of the EGFR/ErbB family of receptor tyrosine kinases. EGFR plays a key role in the regulation of essential normal cellular processes and in the pathophysiology of hyperproliferative diseases such as cancer. Activation of the EGFR signaling pathway has been linked with increased cell proliferation, angiogenesis, metastasis and decreased apoptosis. Thr669 (equivalent to Thr693 of human EGFR) is phosphorylated by p38 MAP kinase following EGF stimulation. Phosphorylation of EGFR at Thr669 may be involved in regulation of ligand induced receptor internalization through interaction with specific downstream EGFR tyrosine kinase substrates.