[Quality control of HER2 immunohistochemistry--results from a Hungarian study]

Whether a breast carcinoma is HER2-positive or -negative has a significant impact on its treatment. The most common method of evaluating the HER2 status of breast tumors is immunohistochemistry. Preliminary data suggest that the proportion of HER2-positive tumors in Hungary shows a wide range from laboratory to laboratory, and overall it just reaches the bottom levels of the incidence reported in the literature (12% 3+ and 11% 2+ cases). A 3-round quality-control test was implemented on a voluntary and anonymous basis. Participating laboratories had to immunostain and evaluate 4 tumor samples per circulation, according to their daily routine. The authors of the present article gave an expert opinion in all cases, and this was compared with the individual laboratories' evaluation and the real FISH-controlled HER2 status of the samples. On the basis of the participants' and experts' evaluation 22/218 and 21/218 HER2 3+ cases were underscored, corresponding to an underevaluation rate of 10%. As most samples were from HER2-positive tumors, overscoring was less common (1%), but reached 5% (individual laboratories' evaluation) or 7% (expert evaluation) when the 2+ scoring of negative cases was also considered. Each case was discussed interactively with the participants and technical advise was also given when deemed necessary. The evaluation of the HER2 status of breast cancers gives reliable results only if adequate quality control measures are implemented, and this study was an important step in this respect.