The EGFR （Epidermal Growth Factor Receptor） is a transmembrane glycoprotein located on the cell membrane and belongs to the ErbB receptor tyrosine kinase family （HER1/ErbB1）. Its structure consists of three main domains: an extracellular region, a transmembrane region, and an intracellular region. The extracellular region contains four domains （I-IV）, with domains II and IV being cysteine-rich and responsible for binding ligands （such as EGF and TGF-α）, leading to receptor dimerization. The transmembrane region is a single α-helix that anchors the receptor in the cell membrane. The intracellular region possesses tyrosine kinase activity and includes a juxtamembrane domain, a kinase domain （with an ATP-binding site）, and a C-terminal regulatory tail containing multiple autophosphorylation sites （e.g., Y992, Y1045, Y1068）. EGFR activates downstream signaling pathways such as RAS/RAF/MEK/ERK and PI3K/AKT, regulating cell proliferation, differentiation, migration, and survival. Mutations or overexpression of EGFR are strongly associated with various cancers, including lung and colorectal cancers, making it a key target for drugs like gefitinib and osimertinib.