HER2 is a protein encoded by the ERBB2 gene.
- Is a 185 kD transmembrane protein with an extracellular ligand binding domain and an intracellular domain with tyrosine kinase activity.
- Is part of the epidermal growth factor receptor (EGFR) family.
- Can be detected by immunohistochemistry (IHC), Western blot, and enzyme-linked immunosorbent assay (ELISA).
- Is expressed normally in breast tissue at low levels.
- Is located on the long arm of chromosome 17 (17q12-12.32).
- Can be detected by fluorescence in situ hybridization (FISH), chromogenic in situ hybridization (CISH), and polymerase chain reaction (PCR).
- Amplification of the gene leads to overexpression of the protein in breast cancer.
- Amplification of the gene is most often the cause of overexpression of the protein in breast cancer, but it is not the only mechanism.