RATIONALE: Antibiotics may stop the growth of Helicobacter pylori which may be associated with gastric lymphoma.

PURPOSE: Phase II trial to study the effectiveness of antibiotic therapy in treating patients with low grade gastric lymphoma that has not been previously treated.

OBJECTIVES: I. Determine the rate of eradication of Helicobacter pylori using omeprazole, colloidal bismuth subcitrate, tetracycline, and metronidazole in patients with low grade gastric lymphoma. II. Determine the macroscopic/endoscopic and microscopic healing/remission rate after eradication of Helicobacter pylori in this patient population. III. Determine the natural history of low grade gastric lymphoma after eradication of Helicobacter pylori.

OUTLINE: This is a nonrandomized, open label, multicenter study. Patients receive oral omeprazole bid on days 1-10, oral bismuth subcitrate and oral tetracycline qid on days 4-10, and oral metronidazole tid on days 4-10. Patients are evaluated at 8 weeks. Patients who experience complete remission and are H. pylori negative proceed to follow up. Patients with complete remission or no change but who are H. pylori positive proceed to a second course of therapy with the previous schedule or with omeprazole bid, amoxicillin qid, and clarithromycin tid for 14 days. Patients who experience no change but are H. pylori negative are followed at 6 and 9 months and restaged. Patients are followed at 6, 9, 12, 18, and 24 months, then annually thereafter.

PROJECTED ACCRUAL: Approximately 60-96 patients will be accrued for this study.

DISEASE CHARACTERISTICS: Histologically proven, previously untreated, low grade gastric lymphoma Clinical stage I and II1 No bulky disease No high grade component (grade 5 and 4, if monoclonality proven, allowed) Documented presence/absence of H. pylori infection Measurable and/or evaluable disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: WHO 0-2 Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Not specified Renal: Not specified Other: Not pregnant or lactating Fertile patients must use effective contraception No prior or concurrent malignancies unless: At least 1 year remission Low risk or recurrence No prior gastric malignancy No nonmalignant disease causing poor medical risk No allergy to omeprazole

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Not specified Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy to the abdomen Surgery: No prior gastric surgery except simple closure of perforated ulcer with or without wedge excision of the ulcer Other: No prior therapy for gastric lymphoma At least 30 days since experimental therapy No other concurrent experimental therapy At least 30 days since antibiotics with activity against H. pylori