Background： A number of studies have examined human epidermal growth factor receptor 2 （HER2） status in primary gastric cancer （GC） and associated metastasis, some showed their great concordance in FIER2 expression, but others demonstrated notable discordance. There is still little consensus on HER2 discordance, therefore, a systematic review and meta-analysis was conducted to assess the status on HER2 discordance between primary GC and its paired metastasis. Methods： PubMed, EMBASE, ASCO and The Cochrane Library were searched for studies that explored the concordance between primary tumor and metastasis in patients with GC up to 10 March, 2014. Data of discordance of HER2 between primary GC and corresponding metastasis were extracted from the publications and random-effects models were used to estimate pooled discordance proportions. Results： Eighteen articles including 1,867 patients were included for the meta-analysis in accordance with the selection criteria. Pooled discordance proportions were 7% [95% confidence interval （CI）： 5-10%] for HER2 status. Pooled proportions of tumors shifting from positive to negative and from negative to positive were 17% （95% CI： 7-29%） and 4% （95% CI： 2-6%） respectively. No publication bias was found in the meta-analysis. Conclusions： The discordance of HER2 status is not rare in primary and metastatic GC through our metaanalysis. Prospective studies are needed to testify the clinical significance of the discordance of HER2 status.
