AIM: To investigate both whether the risk of gastric cancer is associated with the Ile/Val single nucleotide polymorphism (SNP) of human epidermal growth factor receptor-2 (HER-2) transmembrane domain-coding region at codon 655 and the suggested existence of HER-2 expression in gastric cancer cases in a Turkish patient group. METHODS: Polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP) strategy was used to analyze the presence of HER-2 SNP at codon 655. c-erbB-2 expression pattern was analyzed by immunohistochemistry. The results were compared between gastric carcinoma group and chronic gastritis group, as well as between clinicopathological parameters and carcinoma. RESULTS: Results showed that Ile/Val genotype accounted for 20% within the Turkish gastric carcinoma group, and none in chronic gastritis group, and this ge-notyping was associated with stage IV gastric cancers (P = 0.04). Positive membranous HER-2 immunoreac-tivity, on the other hand, accounted for 24% within the Turkish gastric carcinoma group and none from chronic gastritis cases; further, it was correlated with intestinal type carcinomas (P = 0.007), and stage III-IV carcinomas (P = 0.004). CONCLUSION: These observations imply that the tested HER-2 SNP may participate in the development and progression of gastric cancer. Thus, after confirming these results with large sample groups, HER-2 codon 655 SNP and/or c-erbB-2 overexpression may also be used as a poor prognostic indicator for gastric carcinomas. AIM: To investigate both the risk of gastric cancer is associated with the Ile / Val single nucleotide polymorphism (SNP) of human epidermal growth factor receptor-2 (HER-2) transmembrane domain-coding region at codon 655 and the suggested existence of METHODS: Polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP) strategy was used to analyze the presence of HER-2 SNP at codon 655. c-erbB -2 expression pattern was analyzed by immunohistochemistry. The results were compared between gastric carcinoma group and chronic gastritis group, as well as between clinicopathological parameters and carcinoma. RESULTS: Results showed that Ile / Val genotype accounted for 20% within the Turkish gastric carcinoma group , and none in chronic gastritis group, and this ge-notyping was associated with stage IV gastric cancers (P = 0.04). Positive membranous HER-2 immunoreac- tivity, on the other han d, accounted for 24% within the Turkish gastric carcinoma group and none from chronic gastritis cases; further, it was correlated with intestinal type carcinomas (P = 0.007), and stage III-IV carcinomas Thus, after confirming these results with large sample groups, HER-2 codon 655 SNP and / or c-erbB-2 overexpression may also be used as a poor prognostic indicator for gastric carcinomas.