Human epidermal growth factor receptor 2 (HER2, also known as ERBB2, Neu, ErbB-2, CD340 or p185) is a proto-oncogene HER2/neu located on the long arm 17q12 of human chromosome 17. The coding, which is a member of the epidermal growth factor receptor (EGFR/ErbB) family, has tyrosine kinase activity and is involved in signal transduction of cell growth and differentiation. The oncogenic mechanism of the HER2 oncogene includes inhibition of apoptosis, promotion of cell proliferation, increase of invasiveness of tumor cells, and promotion of tumor vascular and lymphangiogenesis. 20% of breast cancer and 12% of gastric cancer patients showed positive HER2 gene amplification.