First-line Antibiotic Therapy for Early-stage HP(+) Gastric Pure DLBCL

Inclusion Criteria: 1. Patients must have histologically confirmed H. pylori-positive primary gastric pure (de novo) gastric DLBCL. 2. Patient must have no prior chemotherapy or radiotherapy for his/her gastric pure (de novo) gastric DLBCL. 3. Patients must have evaluable disease by endoscopy and/or by computed tomography. 4. Patients must have documented H. pylori infection before treatment, if any of the following test show positive result: histology, rapid urease test (CLO-test), C13 urease breath test, and serology. 5. Patients must have either stage IE or IIE-1 disease, according to an adaptation of the Ann Arbor staging system modified by Musshoff for primary extranodal lymphoma. 6. Patients who are either newly diagnosed or already starting anti-H. pylori therapy but not have follow-up endoscopy and biopsy are eligible. 7. Patient must have signed the informed consent, and agree to provide achieved pathologic material for immunohistochemical / fluorescence in situ hybridization study and RT-PCR for t(11;18)(q21;q21) determination. Exclusion Criteria: 1. Patients with extensive gastrointestinal tract involvement. 2. Patients with previous history of extranodal lymphoma. 3. Patients with stage IIE-2 or beyond disease: infiltration of regional lymph node. 4. Patients with cardiopulmonary status that do not allow repeat endoscopy. 5. Patients with prior chemotherapy or radiotherapy for their primary gastric lymphoma. 6. Patients who had previous anti-H. pylori therapy and without pretreatment pathology achieve material for histological review and immunohistochemical study.