Fig. 1

NordiQC HER2 assessment scheme. NordiQC criteria for assessing a HER2 stain as optimal are clear and unequivocal staining reactions corresponding to the 0/1+/2+/3+ IHC scores (as specified by current ASCO/CAP scoring criteria [ASCO/CAP 2007 [10]) obtained in the reference laboratories. A stain is assessed as good if a HER2-amplified 3+ carcinoma or a HER2-unamplified 0/1+ carcinoma reveals a 2+ reaction. A stain is assessed as borderline if the signal-to-noise ratio is low, for example in cases of moderate cytoplasmic reaction, excessive counterstain or excessive retrieval hampering interpretation. A stain is assessed as poor in case of a FN reaction (for example a 3+ carcinoma or a 2+ carcinoma with HER2 gene amplification that reveals a 0 or 1+ reaction) or a FP stain where a 0/1+ or 2+ carcinoma without HER2 gene amplification reveals a 3+ reaction. The inclusion of 2+ cores with and without HER2 gene amplification is considered essential to evaluate the IHC HER2 performance and the robustness of the pathology laboratories’ protocols, as 2+ cores are more likely to reveal FN or FP staining reactions than 3+ or 0/1+ cores, respectively. ASCO, American Society of Clinical Oncology; CAP, College of American Pathologists; IHC, immunohistochemistry; NordiQC; Nordic Immunohistochemistry Quality Control Group