Comparison of HER2 status by fluorescence in situ hybridisation and immunohistochemistry in gastric cancer

To investigate the differences and relevance, and to evaluate the clinical significance of fluorescence in situ hybridisation and immunohistochemistry (IHC) in detecting HER2 in gastric cancer tissues. The expression of HER2 protein and the amplification of the HER2 gene in 118 gastric cancer tissues were detected by immunohistochemistry and fluorescence in situ hybridisation, respectively. Using IHC, we found that in 40 cases (33.9%) the HER2 expression was at level 0, in 33 cases (28.0%) the HER2 expression was at level 1+, in 16 cases (14%) the HER2 expression was at level 2+, and in 29 cases (25.6%) the HER2 expression was at level 3+, respectively. Using the FISH test, 38 of 118 cases (32.2%) were judged as positive results. The concordance rate between the results of IHC and FISH in all cases was 85.6%. The concordance rate of IHC and FISH was high in cases of HER2 expression at level 0, 1+ and 3+ according to IHC, but low in cases of 2+ according to IHC (43.8%). Immunohistochemistry cannot predict HER2 gene amplification accurately. The FISH test should be executed in IHC 2+ cases.