Human epidermal growth factor receptor 2 (HER2) is a Type I membrane glycoprotein and tyrosine kinase that forms part of several cell surface receptor complexes, but it apparently requires a coreceptor for ligand binding. Among ErbB family members, HER2 stands out as unique because it has no identified ligands. Instead, it heterodimerizes with the other members of the ErbB family to form higher affinity signaling complexes. HER2 is widely expressed in epithelial cells and has also been found to be over-expressed in a significant number of breast carcinomas. Approximately 30% of breast cancers have an amplification of HER2 gene or overexpression of its protein product. Furthermore, HER2 regulates outgrowth and stabilization of peripheral microtubules (MTs). The cytoplasmic domain has been shown to associate with beta-catenin and plakoglobin. Additionally, an unidentified protease can cleave HER2 from the cell surface through proteolytic cleavage. It also contributes to development, cancer progression, neuromuscular junction communication, as well as regulation of cell growth and differentiation. Notably, the association between HER2 gene and malignancy along with poor prognosis has been reported in numerous carcinomas, including breast, prostate, ovarian, lung cancers and so on.