Comparison of HER2 status determination methods in HER2 (2Â +) patients: Manual fluorescent in situ hybridization (FISH) vs. dual silver enhanced in situ hybridization (SISH)

•Dual SISH can be used to validate HER2 status in immunohistochemically HER2 (2 +) breast carcinoma.•Preanalytical and analytical problems may cause uninterpretable SISH signals.•Standardization and quality control programs are required to optimize SISH tests.

HER2 amplification has been demonstrated in 15-25% of invasive breast carcinomas and can be assessed using immunohistochemical and in situ hybridization methods. Here, we compared the accuracy of dual SISH to manual FISH in HER2 (2 +) breast carcinoma and evaluated the feasibility of dual SISH method in routine practice. Sixty HER2 (2 +) consecutive tumor samples diagnosed between January 2009 and February 2013 were selected. Demographic, histological and immunohistochemical features and FISH results were recruited from patient records and compared to dual SISH results. Nine (15%) of the 60 tumor samples were excluded from statistical analysis due to lack of interpretable SISH signals. HER2 staining percentages by immunohistochemistry differed between 20 and 80%. HER2 amplification was shown in 7 (13.7%) and 8 (15.7%) patients by FISH and SISH, respectively. Very good agreement was observed between FISH and SISH methods (kappa value: 0.92). Significant correlation was found between HER2 staining percentage and FISH positivity, in contrast to SISH positivity (p = 0.012 vs. p = 0.069). Our results are consistent with previously reported literature, indicating SISH can be used to determine HER2 status. However, preanalytical and analytical problems may cause inadequate or uncountable signals, making interpretation impossible for the pathologist and highlighting the importance of standardization and quality control programs.