Diagnosis typically involves a combination of imaging tests, biopsy, and laboratory tests. A biopsy involves taking a sample of the tumor tissue, which is then tested for the presence of the HER2 protein or the HER2 gene amplification. Common tests include Immunohistochemistry (IHC) and Fluorescence In Situ Hybridization (FISH). An IHC test measures the amount of HER2 protein on the surface of cells, while FISH looks for extra copies of the HER2 gene.
