DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed advanced adenocarcinoma of the colon, rectum, pancreas, esophagus, or stomach that is refractory to standard treatment
• Overexpression of the Lewis-Y antigen
• Measurable or evaluable disease
• No CNS metastasis
• Metastatic liver disease from primary tumor allowed

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• ECOG 0-1

Life expectancy:

• At least 3 months

Hematopoietic:

• Platelet count greater than 100,000/mm^3
• Absolute granulocyte count greater than 1,200/mm^3

Hepatic:

• Bilirubin normal
• SGOT and SGPT no greater than 1.5 times upper limit of normal
• Hepatitis B or C antigen negative
• No liver disease (e.g., alcohol liver disease)
• Albumin at least 3.0 g/dL

Renal:

• Creatinine no greater than 1.4 mg/dL
• Creatinine clearance at least 60 mL/min
• Proteinuria no greater than 1 g/24 hours (grade II toxicity-like)

Cardiovascular:

• No prior coronary artery disease
• No New York Heart Association class II, III, or IV congestive heart failure
• No arrhythmia requiring treatment

Pulmonary:

• FEV_1 and FVC greater than 65% predicted

Other:

• No other concurrent malignancy
• No active peptic ulcer disease
• No known allergy to omeprazole
• No known seizure disorder
• No concurrent medical or psychiatric condition that would preclude study participation
• No contraindication to pressor therapy
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered

Endocrine therapy:

• At least 3 weeks since prior hormonal therapy

Radiotherapy:

• At least 3 weeks since prior radiotherapy and recovered

Surgery:

• Not specified