An evaluation on clinico-pathologic correlation and outcome of human epidermal growth factor receptor 2 subgroups reclassified according to the latest ASCO/CAP guideline

Abstract Background The latest CAP/ASCO guideline has updated the interpretation of uncommon HER2 in situ hybridization patterns (groups 2-4) with concomitant HER2 immunohistochemistry, leading to changes in diagnosis of these subgroups. We sought to assess the clinico-pathologic features and outcome in these subgroups in details with our local cohort. Methods Clinico-pathologic features of groups 2-4 were compared to the typical amplified (group 1: HER2:CEP17≥2, HER2≥4) and non-amplified (group 5: HER2:CEP17 Results Group 2 (HER2:CEP17≥2, HER2 Conclusion Our findings showed more similarities among group 2, 4 and 5 than with group 1 and 3, supporting the HER2 categorization in the latest guideline. Additional studies may be warranted to assess the outcome of these patients with the different managements. Micro-abstract The latest update re-categorized the diagnosis of HER2 uncommon ISH categories. Despite that, there are no robust clinical evidence to support this categorization. In this study, we sought to compare the clinico-pathologic characteristics and outcome of these groups with the typical amplified and non-amplified cases to gain further insights into their biology and the relevance of their revised classification.