What is HER2 breast cancer testing?HER2 stands for human epidermal growth factor receptor 2. It is a gene that makes a protein found on the surface of all breast cells. It is involved in normal cell growth.Genes are the basic units of heredity, passed down from your mother and father. In certain cancers, especially breast cancer, the HER2 gene mutates (changes) and makes extra copies of the gene. When this happens, the HER2 gene makes too much HER2 protein, causing cells to divide and grow too fast.Cancers with high levels of the HER2 protein are known as HER2-positive. Cancers with low levels of the protein are known as HER2-negative. About 20 percent of breast cancers are HER2-positive.HER2 testing looks at a sample of tumor tissue. The most common ways to test tumor tissue are:Immunohistochemistry (IHC) testing measures the HER2 protein on the surface of the cellsFluorescence in situ hybridization (FISH) testing looks for extra copies of the HER2 geneBoth types of tests can tell whether you have HER2-positive cancer. Treatments that specifically target HER2-positive breast cancer can be very effective.Other names: human epidermal growth factor receptor 2, ERBB2 amplification, HER2 overexpression, HER2/neu tests
