Testing for HER2 status

Incorporation of a new biological marker such as HER2 into routine clinical practice requires proof that it provides reproducible information independ ent of, and better than, conventional pathologic criteria, and that it infl uences treatment decisions. In breast cancer, HER2 amplification/overexpres sion predicts for a poor clinical outcome and an enhanced survival benefit from the HER2-targeted therapy, Herceptin (R), and may predict for resistan ce to some conventional therapies. Thus, HER2 is considered to be a clinica lly important molecule and testing for HER2 abnormalities is already part o f routine patient assessment in many parts of the world. There is currently no gold standard for HER2 testing. The main challenge is to standardize an d technically validate HER2 testing methodologies. Immunohistochemistry (IH C) and fluorescence in situ hybridization (FISH) are the most common HER2 t ests used, and show a high level of concordance. HER2 testing approaches ba sed on the polymerase chain reaction (PCR) are under extensive investigatio n and appear promising. A Canadian HER2 testing algorithm designed to incre ase the validity and reproducibility of HER2 testing has been compiled. HER 2-positive cases are defined as those with > 10% of tumor cells with modera te/strong, complete membrane staining in the invasive component, by IHC. Co nfirmatory HER2 testing using either FISH or quantitative PCR is recommende d for indeterminate cases. Additional studies are required to calibrate HER 2 testing results to clinical outcome. Copyright (C) 2001 S. Karger AG, Bas el.