Emerging technologies for HER2 testing

HER2-positive status is the sole criterion for identifying patients with breast cancer for Herceptin therapy, which has known efficacy in women with metastatic breast cancer (MBC). Immunohistochemistry (IHC) and fluorescence in-situ hybridization (FISH), which measure the HER2 protein and gene, respectively, are currently the most widely used HER2 tests in the clinical setting. However, results from these assays are influenced by many variables including choice of antibody or probe, methodology, level of user experience and interlaboratory variability. Although there is no widespread standard testing algorithm, the importance of HER2 in clinical practice demands accurate and reproducible tests. Polymerase chain reaction (PCR) and chromogenic in-situ hybridization (CISH) represent upcoming methods for assessing HER2 gene amplification. Enzyme-linked immunosorption assay (ELISA), a semi-automated technique that can be used to measure the level of the HER2 extracellular domain (ECD) in serum, may also prove useful. While such technologies show great promise, they will at least have to be validated against IHC or FISH before being accepted into routine clinical practice.