 The study will validate the use of antibiotics as first-line therapy for stage IE and perhaps IIE-1 Hp-positive gastric pure de novo DLBCL. The status of NF-kB, BCL10, BAFF, and CagA IHC nuclear staining will help to tailoring the treatment for early-stage gastric pure de novo DLBCL. And 50-60 of stage IE IIE-1 pure de novo DLBCL patients can be cured by 2-weeks of antibiotics rather than the 6-months of relatively toxic front-line systemic chemotherapy. The investigators shall also elucidate the distribution of CYP2C1819 in patients with pure de novo DLBCL and their association with the efficacy of sequential antibiotics for eradication of Hp infection. 