[Immunochemistry evaluation of HER2 status in infiltration breast cancer: technical protocol and interpretation...

In Europe, patients who may benefit from Herceptin((R)) (an HER2 targeted drug) are currently selected by immunohistochemistry (IHC). Reliable detection of HER2 status is essential to the appropriate usage of Herceptin(R), because its specificity is limited to tumours overexpressing HER2. It is essential that the IHC evaluation of the HER2 status of a mammary carcinoma be optimized and reliable. This technical paper reviews the different steps of the IHC technique, the controls and, the rules for interpretation. The sensitivity of the IHC technique must be adjusted so as not to produce false negatives or false positives. As opposed to other methods, it can be carried out whatever the fixation conditions of the tissues. The interpretation of the immunostains also requires training; it is fraught with problems for intermediate positivities. The ideal score to evaluate HER2 status has not yet been defined. It will thus be necessary to report the percentage of stained cells, the intensity of the staining, and, in respect to Herceptin((R)) treatment, the HercepTest scoring system (recommended in the package insert). Once acquired, this knowledge must be perpetuated by the observation of rules of good technical practice (internal and external controls, quality assurance programs). FISH should be used for complementary assessment of 2+ cases (on condition that they have not been fixed in Bouin's liquid) and for the calibration of the IHC technique.