Concordance of HER2 status tested by IHC and FISH in biopsy and surgical resection specimens and comparison with clinicopathological features in gastric carcinoma

Context: HER2-targeted therapy has been shown to benefit HER2-positive gastric cancer. It is very important to determine the HER2 expression level correctly to select the appropriate test and sampling method. Aim: In this study, we investigated the frequency of overexpression of HER2 and intratumoral heterogeneity of HER2-positive cases, comparison of HER2 used immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) performance in biopsy and resection specimens, the correlation of HER2 status between biopsy and resection specimens, and its relationship with clinicopathological findings. Materials and Methods: Formalin-fixed, paraffin-embedded specimens of a total of 40 surgically resected and biopsy specimens of gastric cancer were analyzed. HER2 status was examined using both IHC and FISH techniques, and the findings and their association with different clinicopathological parameters were evaluated. Results: The concordance rate between the results of IHC and FISH in biopsy and resection specimens was 96.6% and 86.6%, respectively. In paired 20 cases, the overall concordance rate of HER2-IHC and HER2-FISH status between biopsy and resection specimens was 90% and 100%, respectively. HER2-IHC analysis revealed that 5/40 cases were IHC 2+ and only 1 of 5 IHC 2+ cases demonstrated HER2-FISH amplification. Conclusion: Our results showed that HER2-IHC was well concordant with FISH in cases with a score of 0/1+ or 3+ and demonstrates strong concordance between biopsy and resection specimens. FISH should be performed when the IHC result is equivocal. In our study, no statistically significant correlation was observed between HER2 positivity and clinicopathological parameters. Overall, both biopsy and resection specimens are appropriate for HER2 testing.