Background Accurate detection of human epidermal growth factor receptor 2 (HER2) expression and gene amplification is crucial for the application of HER2-specific therapy and for evaluating the response of patients with breast cancer.A uniform and standard procedure of immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) needs to be established for evaluating the HER2 status in breast cancer tissues for the treatment of patients with real HER2-positive tumors.The present multicenter study was aimed to examine the HER2 status in breast cancer specimens from Chinese patients using both IHC and FISH methods.Methods A multicenter study was performed on the HER2 status in 3 149 breast cancer specimens from different ethnic populations and areas in China by IHC and FISH assays.The potential association of HER2 status with demographic and clinical characteristics was analyzed.Results The positive rates for HER2 over-expression and HER2 amplification were 23.3％ and 27.5％ in this study,respectively.The concordance between IHC and FISH was 71.2％ (K=0.494,P ＜0.001).Furthermore,72.9％ of specimens with IHC 2+ were negative to FISH.The discordance rates among laboratories were from 5％ to 28％ for IHC and 1％ to 16％ for FISH.HER2 amplification was associated significantly with advanced tumor stage (Ⅲ or Ⅳ,P=0.002),large tumor size (＞5 cm,P=0.002),moderate and poor histological grades (P ＜0.0001),post-menopause (P ＜0.0001),ER-PR-(P=0.002),and having ＞4 lymph nodes affected (P ＜0.0001) in this population.The positive rates of HER2 amplification in specimens from Man and Hui Chinese were significantly higher than that in other Chinese populations.There are slightly higher positive rates of HER2 expression and amplification in Chinese patients with breast cancer.Conclusion These findings may provide new insights into understanding the epidemiological features of HER2 expression and amplification,and may be valuable for clinical practice.