RATIONALE: Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. It is not yet known whether chlorambucil is more effective than observation in treating low-grade lymphoma of the stomach.

PURPOSE: Randomized phase III trial to compare the effectiveness of chlorambucil with that of no further therapy following anti-Helicobacter therapy in treating patients with low-grade lymphoma of the stomach.

OBJECTIVES: I. Determine the efficacy and response rate of triple antibiotic therapy for Helicobacter pylori in the healing of lesions in patients with low grade gastric lymphoma. II. Assess the efficacy of chlorambucil in the prevention of relapse in patients after complete eradication of low grade gastric lymphoma. III. Determine the natural history of unresected or partially resected low grade gastric lymphoma treated medically.

OUTLINE: This is a randomized study. Patients are randomized to receive chlorambucil or placebo. Patients receive omeprazole daily for 1 week. Clarithromycin and tinidazole are administered twice daily for 1 week for the eradication of H. pylori infection. Patients are assessed every 2-3 months by endoscopy. Patients may receive a maximum of 3 courses of treatment every 2-3 months. Other regimens may be used if full eradication of H. pylori is not achieved. Patients who achieve complete response (eradication of H. pylori) are randomized to receive oral chlorambucil or placebo daily for 14 days. Treatment is repeated every 28 days for 6 courses. Patients are followed every 6 months for 2 years, then yearly thereafter.

PROJECTED ACCRUAL: A total of 200 patients will be accrued for this study.

DISEASE CHARACTERISTICS: Endoscopically diagnosed, unresected, partially resected, or completely resected low grade (stage I) gastric lymphoma Prior diagnosis of H. pylori infection No nodal metastases Microbiological evidence of current H. pylori infection required No pathological evidence of enlarged abdominal lymph nodes by CT scan Gastroscopic ultrasound evidence of enlarged nodes allowed, if CT scan normal

PATIENT CHARACTERISTICS: Age: 16 and over Performance status: Not specified Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Not specified Renal: Not specified

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Not specified Endocrine therapy: Not specified Radiotherapy: Not specified Surgery: See Disease Characteristics