Today, immunohistochemistry and FISH are the most commonly used clinical methods for determining HER2 status in breast cancer, and these techniques, as well as alternative ISH methods, are currently recommended by the ASCO/CAP.8 Generally, FISH analysis is considered the gold standard in HER2 testing;18 however, as outlined in the Introduction, there are several limitations and disadvantages of this technique, many of which can be ameliorated by the use of CISH. This evidence concerns the gene ERBB2 and breast cancer.