GRB2 and gastric cancer: To evaluate the hypotheses, a two-stage genetic analysis that focused on genes which directly encode CagA-binding molecules, SRC, PTPN11, CRK, CRKL, CSK, c-MET and GRB2, was conducted that included: 1) the discovery phase that screened and identified single nucleotide polymorphisms (SNPs) with a significant genetic association on gastric cancer; 2) the extension phase that re-analyzed the most significant SNPs in the discovery phase.