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HER2 activation results from heterodimerization with another ERBB member or by homodimerization when HER2 concentration are high, for instance in cancer. [8] Amplification or over-expression of this oncogene has been shown to play an important role in the development and progression of certain aggressive types of breast cancer .
The overexpression of HER2 is determined by immunohistochemistry (IHC), or with fluorescent in situ hybridization in those equivocal cases where IHC does not provide a clear result. Different molecular subtypes of breast cancer have also been described, which loosely align with receptor status: Luminal A (ER and/or PR positive; HER2 negative)
ErbB2 overexpression can occur in breast, ovarian, bladder, non-small-cell lung carcinoma, as well as several other tumor types. [28] Trastuzumab or Herceptin inhibits downstream signal cascades by selectively binding to the extracellular domain of ErbB-2 receptors to inhibit it. [28] This leads to decreased proliferation of tumor cells. [28]
The epidermal growth factor receptor is a member of the ErbB family of receptors, a subfamily of four closely related receptor tyrosine kinases: EGFR (ErbB-1), HER2/neu (ErbB-2), Her 3 (ErbB-3) and Her 4 (ErbB-4). In many cancer types, mutations affecting EGFR expression or activity could result in cancer. [6]
Overexpression of HER2 sidesteps these checkpoints, causing cells to proliferate in an uncontrolled fashion. [44] Trastuzumab binds to domain IV of the [62] extracellular segment of the HER2/neu receptor. Monoclonal antibodies that bind to this region have been shown to reverse the phenotype of HER2/neu expressing tumor cells. [63]
Triple-negative breast cancer (TNBC) is any breast cancer that either lacks or shows low levels of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) overexpression and/or gene amplification (i.e. the tumor is negative on all three tests giving the name triple-negative). [1]
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