HER2 status testing by immunohistochemical and fFluorescence in situ hybridization in China

e22233 Background: HER2 gene overexpression is associated with aggressive breast cancer and poor clinical prognosis. Humanized anti-HER2 monoclonal antibody trastuzumab, which is targeted HER2 protein has showed to improve overall survival in patients with HER2-positive breast cancer in both the metastatic and adjuvant settings. There are some differences in HER2 positive rate among difference reports in China. This study tested HER2 status by immunohistochemistry(IHC) and fluorescence in situ hybridization (FISH) and compared HER2 testing at central and regional laboratories in China. Methods: Assessment of HER2 status was performed by FISH using the HercepTeast kit at central laboratory and by IHC using commercial available anti-HER2 probe in formalin-fixed and paraffin-embedded tissue section of 280 breast cancer samples. IHC HER2 testing was performed on 149 samples in the central laboratory. IHC HER2 testing was performed on 80 samples at both central laboratory and regional laboratory. Results: 280 samples were tested 373 times testing by IHC and FISH. The results were showed in table 1 . 80 samples was tested by IHC at central and regional laboratory and testing results of 36.4% samples were accordant (K=0.038). 94.1% IHC3+ at central laboratory were HER2 FISH positive and 83.3% IHC 3+ at regional laboratory were HER2 FISH positive. 86.7% IHC 2+ at central laboratory were HER2 FISH positive and 62.7% IHC 2+ at regional laboratory were HER2 FISH positive. 17 samples were observed HER2 FISH positive in the 27 IHC 0/1+ tested at regional laboratoty. So good correlation was obsearved between FISH HER2 status and IHC results from central laboratory but not from regional laboratory. Conclusions: This study emphasized the important of accurate HER2 testing. HER2 FISH test should be performed for the IHC 2+ samples. Even HER2 FISH test maybe performed for IHC 0/1 sample according to clinical characteristics in China in order to make the patients have targeted therapy chance. [Table: see text] No significant financial relationships to disclose.