Some case reports have demonstrated the heterogeneity of HER2 amplification in primary tumour, or discordant status between primary and metastatic lesions with regard to trastuzumab therapy in breast cancer patients.23,24 However, little is known of this topic in GC, although one IHC study showed that heterogeneity in GC is greater than that found in breast cancer.22 To clarify this issue, we collected 325 cases of primary GCs (cohort A) and 250 cases of metastatic carcinomas with their paired primary carcinomas (cohort B, C and D) and performed HER2 analysis by IHC and FISH. This evidence concerns the gene ERBB2 and breast cancer.