OBJECTIVES: I. Determine a safe and immunogenic combination of G17DT with cisplatin and fluorouracil in patients with chemotherapy-naive metastatic or locally recurrent gastric or gastroesophageal cancer. II. Determine the safety profile and tolerability of this regimen in these patients. III. Determine the tumor response rate, disease stabilization, best overall response, time to progression, time to treatment failure, and overall survival in patients treated with this regimen. IV. Determine the correlation of immunological response with clinical efficacy and benefit in patients treated with this regimen. V. Determine the pharmacokinetics and pharmacodynamics of this regimen in these patients.

OUTLINE: This is a multicenter study. Patients are assigned to one of four treatment regimens. Regimen A: Patients receive high-dose G17DT intramuscularly (IM) on days 7, 35, and 63. Patients also receive cisplatin IV over 1-3 hours on day 1 followed by fluorouracil IV continuously over days 1-5 every 4 weeks in the absence of disease progression or unacceptable toxicity. If inadequate immune response is seen on Regimen A, subsequent patients are treated on Regimen B. If unacceptable toxicity is seen on Regimen A, subsequent patients are treated on Regimen C. If inadequate immune response and unacceptable toxicity are seen on Regimen A, or if unacceptable toxicity is seen on Regimen B or inadequate immune response is seen on Regimen C, then subsequent patients are treated on Regimen D. Regimen B: Patients receive high-dose G17DT IM on days 1, 28, and 56. Patients also receive cisplatin IV over 1-3 hours on day 35 followed by fluorouracil IV continuously over days 35-39 every four weeks in the absence of disease progression or unacceptable toxicity. Regimen C: Patients receive low-dose G17DT IM on days 7, 35, and 63 with chemotherapy as in regimen A. Regimen D: Patients receive low-dose G17DT IM on days 1, 28, and 56 with chemotherapy as in regimen B. Quality of life is assessed at baseline, on day 7, every 2 weeks for 10 weeks, and then every 4 weeks thereafter.

PROJECTED ACCRUAL: A total of 15-75 patients will be accrued for this study within 5-30 months.

DISEASE CHARACTERISTICS: Histologically confirmed gastric adenocarcinoma including adenocarcinoma of the esophagogastric junction Diffuse type Intestinal type Linitis Metastatic disease (cytological or histological confirmation required if metastatic lesion is sole site of disease) OR Locally recurrent disease if at least 1 measurable lesion (e.g., lymph node) Measurable disease No CNS metastasis

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 80-100% Life expectancy: More than 3 months Hematopoietic: Hemoglobin at least 10 g/dL Absolute neutrophil count at least 2,000/mm3 Platelet count at least 100,000/mm3 No active disseminated intravascular coagulation Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) AST and ALT no greater than 2.5 times ULN Alkaline phosphatase no greater than 2.5 times ULN Renal: Creatinine normal No hypercalcemia Cardiovascular: No unstable cardiac disease despite treatment No myocardial infarction within the past 6 months Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No other prior or concurrent malignancy except adequately treated carcinoma in situ of the cervix or nonmelanoma skin cancer No primary or acquired immunodeficiency No symptomatic peripheral neuropathy grade 2 or greater No severe hearing disorder No known dihydropyrimidine dehydrogenase (DPD) deficiency No history of significant neurologic or psychiatric disorders including dementia or seizures No active uncontrolled infection No other serious underlying medical condition that would preclude study

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior anticancer immunotherapy At least 1 year since prior bone marrow transplantation Chemotherapy: No prior palliative, adjuvant, or neoadjuvant chemotherapy No other concurrent anticancer chemotherapy No concurrent drugs that could interact with fluorouracil (e.g., cimetidine, allopurinol, or leucovorin calcium) Endocrine therapy: At least 30 days since prior systemic corticosteroids No concurrent corticosteroids except inhaled corticosteroids for asthma or chronic obstructive pulmonary disease or dexamethasone as anti-emetic Radiotherapy: At least 6 weeks since prior radiotherapy No concurrent radiotherapy except localized radiotherapy for bone pain control or other reasons with no curative intent Surgery: At least 3 weeks since prior surgery Other: No prior experimental drugs At least 30 days since prior immunosuppressants No concurrent immunosuppressants No other concurrent investigational drugs No other concurrent anticancer treatment No concurrent amifostine