HER1, also referred to EGFR (Epidermal growth factor receptor), ErbB1 or ErbB, is a type I transmembrane glycoprotein involved in normal growth. It belongs to a member of the receptor tyrosine kinase superfamily and makes up the ErbB family with HER2/neu (ErbB-2), HER3 (ErbB-3) and HER4 (ErbB-4). The HER gene is encoded on chromosome 7p11.2 and activated by binding to specific protein ligands, such as epidermal growth factor (EGF) and transforming growth factor α (TGF-α). Ligand binding induces HER1 dimerizations resulting in protein-tyrosine kinase activation and cellular signaling. This receptor also plays a role in carcinogenic responses and the increased expression of it in most cases is predictive of tumor progression. HER3 (Human epidermal growth factor receptor 3), also referred to ERBB3, ErbB-3, LCCS2, Erb-b2 receptor tyrosine kinase 3 or receptor tyrosine-protein kinase erbB-3, is a membrane-bound protein with a neuregulin binding domain (not an active kinase domain). It is encoded by the human ERBB3 gene mapping at the chromosome 12q13.2. HER3 acts as a cell surface receptor for neuregulins and belongs to the epidermal growth factor receptor (EGFR/ERBB) family of receptor tyrosine kinase. Regulation of HER3 expressions and signal transductions involve many interacting proteins, including PI3K, Shc, Nrdp1, and E3 ubiquitin ligases NEDD4. Overexpression of this gene has been reported in various cancers, such as bladder, prostate, and breast tumors. This receptor is emerging as a molecule target for increasing cancers.