Immunohistochemical HER2 Status Evaluation in Breast Cancer Pathology Samples: A Multicenter, Parallel-Design Concordance Study

Objective: As patients with increased human epidermal growth factor receptor (HER2) overexpression are more likely to benefit from trastuzumab treatment, the accuracy of HER2 receptor status in breast cancer patients is significant for appropriate disease management. However, this assessment is not harmonized and results may be highly variable between centers. the aim of this study was to investigate the degree of interlaboratory variability in the results of HER2 expression reported by 5 participating centers and to assess the concordance between these centers and a reference laboratory. Materials and Methods: A total of 30 breast cancer samples were tested and scored for HER2 expression using immunohistochemical method in 5 centers from Turkey and in a reference laboratory from Netherlands (Academic Medical Center, Amsterdam). All the participating centers had an experience of more than 10 years regarding the HER2 testing. the results were compared both among the centers and with the reference laboratory. Results: When the concordance of participating centers and the reference laboratory was evaluated regarding negative (0-1+), equivocal 2(+) and positive 3(+) classification of HER2 immunostaining, the highest concordance was found in Center-A, and the lowest in Center-C (Kendall's tau-b concordance coefficient 0.911 and 0.724, respectively). the concordance of the centers with reference laboratory was 80.0% both in equivocal and positive samples, while it increased up to 91.8% in negative samples. Conclusions: This study showed that in general there is sufficiently good agreement between the reference laboratory and the participating centers for immunohistochemical HER2 assessment