Methodologies

HER2 status can be tested by IHC, which uses antibodies to determine the level of HER2 protein expression, or ISH techniques (including fluorescence, chromogenic and silver ISH), which employ DNA probes to determine the level of HER2 gene amplification. Samples are classified as HER2 positive if they are IHC 3 or have a positive result with ISH.

IHC assessment of HER2 status is subjective, with scoring on a 0–3 scale.

Figure 5.1 Commercial HercepTest™ kit (Dako) scoring system for immunohistochemical characterisation of HER2 status in breast tumoursa (reproduced with permission from Dako)