HER2

Receptor tyrosine-protein kinase erbB-2 is a protein that normally resides in the membranes of cells and is encoded by the ERBB2 gene. ERBB is abbreviated from erythroblastic oncogene B, a gene originally isolated from the avian genome. The human protein is also frequently referred to as HER2 (human epidermal growth factor receptor 2) or CD340 (cluster of differentiation 340). HER2 is a member of the human epidermal growth factor receptor (HER/EGFR/ERBB) family. But contrary to other members of the ERBB family, HER2 does not directly bind ligand. HER2 activation results from heterodimerization with another ERBB member or by homodimerization when HER2 concentration are high, for instance in cancer. 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. In recent years the protein has become an important biomarker and target of therapy for approximately 30% of breast cancer patients.

Receptor tyrosine-protein kinase erbB-2 is a protein that normally resides in the membranes of cells and is encoded by the ERBB2 gene. ERBB is abbreviated from erythroblastic oncogene B, a gene originally isolated from the avian genome. The human protein is also frequently referred to as HER2 (human epidermal growth factor receptor 2) or CD340 (cluster of differentiation 340). HER2 is a member of the human epidermal growth factor receptor (HER/EGFR/ERBB) family. But contrary to other members of the ERBB family, HER2 does not directly bind ligand. HER2 activation results from heterodimerization with another ERBB member or by homodimerization when HER2 concentration are high, for instance in cancer. 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. In recent years the protein has become an important biomarker and target of therapy for approximately 30% of breast cancer patients. ===Immunohistochemistry=== By immunohistochemistry, the sample is given a score based on the cell membrane staining pattern. Micrographs showing each score: File:HER2 immunohistochemistry with 0 pattern.png|0 File:HER2 immunohistochemistry with 1 plus pattern.png|1+ File:HER2 immunohistochemistry with 2 plus pattern.png|2+ File:HER2 immunohistochemistry with 3 plus pattern.png|3+ ===Fluorescence in situ hybridisation=== FISH can be used to measure the number of copies of the gene which are present and is thought to be more reliable than immunohistochemistry. It usually uses chromosome enumeration probe 17 (CEP17) to count the amount of chromosomes. Hence, the HER2/CEP17 ratio reflects any amplification of HER2 as compared to the number of chromosomes. The signals of 20 cells are usually counted. File:HER2 FISH with 2 HER2 signals and 3 CEP17 signals.png|This cell displays 2 signals of HER2 (red) and 3 signals of CEP17 (green) File:Counting one or two signals on HER2 FISH.png|Two signals that are closer to each other than the signal diameter count as one. File:HER2 FISH with debris.png|One of these signals is too faint, and is presumably debris. File:HER2 FISH with only one signal type.jpg|Cells with only one type of signal are excluded from the count. File:HER2 FISH with overlapping cells.png|Overlapping cells are also excluded from the count. File:HER2 FISH with a yellow signal.png|A yellow signal counts as one red and one green (which are overlapping) File:Counting HER2 versus CEP17 probes in FISH of HER2 amplified cell.png File:HER2 FISH algorithm.svg|Algorithm for the evaluation of HER2 on fluorescence in situ hybridization (FISH). If the initial HER2 result is negative for a needle biopsy of a primary breast cancer, a new HER2 test may be performed on the subsequent breast excision.

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