The acronym "HER2" is derived from the full name human epidermal growth factor receptor 2. HER2 is also sometimes referred to as ERB2 or HER2/neu. The "neu" actually refers to a rat antibody homolog. HER2 receptor is encoded by the C-erbB2 gene, and is one of four oncoproteins belonging to the human epidermal growth factor receptor family (HER2 1-4) of the tyrosine kinases. HER2 is over-expressed in approximately 20% of invasive breast cancer cases. Over-expression is localized to chromosome 17 and is associated with more aggressive growth of the tumor. HER2 over-expression is also associated with poor prognosis and resistance to certain chemotherapeutic agents.
The over-expression or activation of HER2 causes amplification, leading to a signal cascade that increases cell proliferation associated with tumor proliferation, that proceeds in a cascade effect as illustrated below: Gene Amplification → Increased Transcription → Increased Expression → Growth & Proliferation