HER2 is a protein that helps a cell grow. The protein sits on the outside of a cell and it can be switched on or off by proteins made by other nearby cells. Different kinds of cells throughout the body make this protein and use it to help them grow.
Another name for this protein is Her2/neu.
Some cancers make extra amounts of HER2 receptor which allows them grow faster than normal cells. A patient with a tumour that makes extra protein will likely benefit from medications that block the action of HER2 such as trastuzumab.
Cancers that make extra HER2 include:
Pathologists can perform tests to see how much HER2 protein a group of cells are making. One type of test is called immunohistochemistry and it allows the pathologist to see the protein on the outside of the cell. This test is given a score of 0 through 3.
Immunohistochemistry scores for HER2:
Pathologists can also determine how much HER2 a cell is making by performing a test called fluorescence in situ hybridization (FISH). Instead of looking for HER2 on the outside of the cell, FISH uses a probe which sticks to the part of the DNA in a cell that tells a cell how to make HER2.
Tumour cells that make extra HER2 will also have more DNA instructions for HER2. Pathologists call this change a translocation.
FISH results for HER2: