DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed gastric or gastroesophageal junction adenocarcinoma

  • Metastatic or inoperable locally advanced disease

• Measurable disease

  • At least 1 unidimensionally measurable lesion at least 20 mm by conventional techniques OR at least 10 mm by spiral CT scan
• No known brain metastases

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• ECOG 0-2

Life expectancy

• At least 12 weeks

Hematopoietic

• Absolute neutrophil count ≥ 1,500/mm^3
• Platelet count ≥ 100,000/mm^3
• Hemoglobin ≥ 9.5 g/dL

Hepatic

• AST and ALT ≤ 2 times upper limit of normal
• Bilirubin ≤ 1.5 mg/dL

Renal

• Creatinine ≤ 1.5 mg/dL OR
• Creatinine clearance ≥ 60 mL/min

Cardiovascular

• No New York Heart Association class III or IV heart disease
• No symptomatic congestive heart failure
• No unstable angina pectoris
• No cardiac arrhythmia

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception during and for 6 months after study participation
• Able to take oral medications
• No prior allergic reaction to compounds of similar chemical or biological composition to oxaliplatin, irinotecan, or capecitabine
• No known hypersensitivity to fluorouracil
• No concurrent uncontrolled illness
• No neuropathy grade 3 or greater
• No active or ongoing infection
• No psychiatric illness or social situation that would preclude study compliance

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No concurrent sargramostim (GM-CSF)

Chemotherapy

• More than 4 weeks since prior chemotherapy and recovered
• No more than 1 course of prior neoadjuvant chemotherapy and/or adjuvant chemotherapy with or without radiotherapy as primary treatment
• No prior chemotherapy for metastatic or recurrent disease

Endocrine therapy

• Not specified

Radiotherapy

• See Chemotherapy
• More than 4 weeks since prior radiotherapy and recovered

Surgery

• Not specified

Other

• At least 4 weeks since prior anticancer therapy
• No concurrent combination antiretroviral therapy for HIV-positive patients
• No other concurrent investigational or commercial agents
• No other concurrent anticancer therapy