3+ HER2 breast cancer detected with the Dako HercepTest. Image courtesy of Jim Burchette.
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