RATIONALE: Chemoprevention is the use of certain drugs or supplements to keep cancer from forming, growing, or coming back. The use of omeprazole and amoxicillin and/or vitamin and mineral supplements and/or garlic supplements may prevent stomach cancer.

PURPOSE: This randomized clinical trial is studying omeprazole and amoxicillin and/or vitamin and mineral supplements and/or garlic supplements to see how well they work in preventing stomach cancer in patients with precancerous stomach lesions.

OBJECTIVES:

Primary

• Compare the effectiveness of omeprazole and amoxicillin and/or vitamin and mineral supplementation comprising beta carotene, vitamin E, ascorbic acid, and selenium and/or garlic supplementation, in terms of lowering the prevalence of severe chronic atrophic gastritis, intestinal metaplasia, dysplasia, and gastric cancer in patients with precancerous gastric lesions.

Secondary

• Compare the effects of these regimens on the rates of transition among the precancerous histopathologic states in these patients.
• Compare the rate of Helicobacter pylori (H. pylori) eradication and reinfection in patients treated with these regimens.
• Compare the effect of these regimens on blood pressure in these patients.

OUTLINE: This is a randomized, double-blind, placebo-controlled study. Patients are stratified according to Helicobacter pylori (H. pylori) antibody status (positive vs negative) and gender. Patients with an initial H. pylori infection are randomized to 1 of 8 treatment arms (I-VIII). Patients testing negative for H. pylori are randomized to 1 of 4 treatment arms (IX-XII).

• Arm I: Patients receive oral omeprazole placebo and oral amoxicillin placebo twice daily for 2 weeks. Three months later, patients are re-evaluated for H. pylori infection. Patients with persistent H. pylori infection receive omeprazole placebo and amoxicillin placebo for an additional 2 weeks. Patients also receive oral vitamin and mineral supplement placebos comprising beta carotene placebo, vitamin E placebo, ascorbic acid placebo, and selenium placebo twice daily and oral garlic supplement placebo twice daily beginning after completion of the initial 2-week treatment period with omeprazole and amoxicillin placebos and continuing for 39 months.
• Arm II: Patients receive omeprazole and amoxicillin placebos and vitamin and mineral supplement placebos as in arm I. Patients also receive an oral garlic supplement twice daily beginning after completion of the initial 2-week treatment period with omeprazole and amoxicillin placebos and continuing for 39 months.
• Arm III:Patients receive omeprazole and amoxicillin placebos as in arm I. Patients also receive oral vitamin and mineral supplements comprising beta carotene, vitamin E, ascorbic acid, and selenium twice daily beginning after completion of the initial 2-week treatment period with omeprazole and amoxicillin placebos and continuing for 39 months and garlic supplement placebo as in arm I.
• Arm IV: Patients receive omeprazole and amoxicillin placebos as in arm I. Patients also receive vitamin and mineral supplements as in arm III and garlic supplement as in arm II.
• Arm V: Patients receive oral omeprazole and oral amoxicillin twice daily for 2 weeks. Three months later, patients are re-evaluated for H. pylori infection. Patients with persistent H. pylori infection receive omeprazole and amoxicillin for an additional 2 weeks. Patients also receive vitamin and mineral supplement placebos and garlic supplement placebo as in arm I.
• Arm VI: Patients receive omeprazole and amoxicillin as in arm V. Patients also receive vitamin and mineral supplement placebos as in arm I and garlic supplement as in arm II.
• Arm VII: Patients receive omeprazole and amoxicillin as in arm V. Patients also receive vitamin and mineral supplements as in arm III and garlic supplement placebo as in arm I.
• Arm VIII: Patients receive omeprazole and amoxicillin as in arm V. Patients also receive vitamin and mineral supplements as in arm III and garlic supplement as in arm II.
• Arm IX: Patients receive omeprazole and amoxicillin placebos, vitamin and mineral supplement placebos, and garlic supplement placebo as in arm I.
• Arm X: Patients receive omeprazole and amoxicillin placebos and vitamin and mineral supplement placebos as in arm I. Patients also receive garlic supplement as in arm II.
• Arm XI: Patients receive omeprazole and amoxicillin placebos as in arm I. Patients also receive vitamin and mineral supplements as in arm III and garlic supplement placebo as in arm I.
• Arm XII: Patients receive omeprazole and amoxicillin placebos as in arm I. Patients also receive vitamin and mineral supplements as in arm III and garlic supplement as in arm II.

After completion of study treatment, patients are followed at 3 months.

PROJECTED ACCRUAL: Approximately 3,600 patients (approximately 2,400 randomized to arms I-VIII [patients with Helicobacter pylori (H. pylori) infection] and 1,000 randomized to arms IX-XII [patients without H. pylori infection]) will be accrued for this study.

DISEASE CHARACTERISTICS:

• Histologically confirmed precancerous gastric lesions by gastroscopic examination
• Gastroscopic results must have been obtained through prior participation in an endoscopic survey conducted in Lindqu, Shandong Province, China
• At high risk for gastric cancer
• Resident of Lindqu, Shandong Province, China

PATIENT CHARACTERISTICS:

Age

• 35 to 69

Performance status

• Not specified

Life expectancy

• Not specified

Hematopoietic

• No history of bleeding disorder

Hepatic

• No liver disease

Renal

• No renal disease

Cardiovascular

• No heart failure

Pulmonary

• No emphysema

Other

• Not pregnant
• No allergy to penicillin or similar drugs
• No cancer except resected nonmelanoma skin cancer
• No other life-threatening illness

PRIOR CONCURRENT THERAPY:

Biologic therapy

• Not specified

Chemotherapy

• Not specified

Endocrine therapy

• Not specified

Radiotherapy

• Not specified

Surgery

• Not specified

Other

• No prior treatment for Helicobacter pylori (H. pylori) infection
• No concurrent regular use of vitamin or mineral supplements