DISEASE CHARACTERISTICS:<br/><br/>          -  Histologically or cytologically confirmed advanced adenocarcinoma of the colon,<br/>             rectum, pancreas, esophagus, or stomach that is refractory to standard treatment<br/><br/>          -  Overexpression of the Lewis-Y antigen<br/><br/>          -  Measurable or evaluable disease<br/><br/>          -  No CNS metastasis<br/><br/>          -  Metastatic liver disease from primary tumor allowed<br/><br/>        PATIENT CHARACTERISTICS:<br/><br/>        Age:<br/><br/>          -  18 and over<br/><br/>        Performance status:<br/><br/>          -  ECOG 0-1<br/><br/>        Life expectancy:<br/><br/>          -  At least 3 months<br/><br/>        Hematopoietic:<br/><br/>          -  Platelet count greater than 100,000/mm^3<br/><br/>          -  Absolute granulocyte count greater than 1,200/mm^3<br/><br/>        Hepatic:<br/><br/>          -  Bilirubin normal<br/><br/>          -  SGOT and SGPT no greater than 1.5 times upper limit of normal<br/><br/>          -  Hepatitis B or C antigen negative<br/><br/>          -  No liver disease (e.g., alcohol liver disease)<br/><br/>          -  Albumin at least 3.0 g/dL<br/><br/>        Renal:<br/><br/>          -  Creatinine no greater than 1.4 mg/dL<br/><br/>          -  Creatinine clearance at least 60 mL/min<br/><br/>          -  Proteinuria no greater than 1 g/24 hours (grade II toxicity-like)<br/><br/>        Cardiovascular:<br/><br/>          -  No prior coronary artery disease<br/><br/>          -  No New York Heart Association class II, III, or IV congestive heart failure<br/><br/>          -  No arrhythmia requiring treatment<br/><br/>        Pulmonary:<br/><br/>          -  FEV_1 and FVC greater than 65% predicted<br/><br/>        Other:<br/><br/>          -  No other concurrent malignancy<br/><br/>          -  No active peptic ulcer disease<br/><br/>          -  No known allergy to omeprazole<br/><br/>          -  No known seizure disorder<br/><br/>          -  No concurrent medical or psychiatric condition that would preclude study<br/>             participation<br/><br/>          -  No contraindication to pressor therapy<br/><br/>          -  Not pregnant or nursing<br/><br/>          -  Negative pregnancy test<br/><br/>          -  Fertile patients must use effective contraception<br/><br/>        PRIOR CONCURRENT THERAPY:<br/><br/>        Biologic therapy:<br/><br/>          -  Not specified<br/><br/>        Chemotherapy:<br/><br/>          -  At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and<br/>             recovered<br/><br/>        Endocrine therapy:<br/><br/>          -  At least 3 weeks since prior hormonal therapy<br/><br/>        Radiotherapy:<br/><br/>          -  At least 3 weeks since prior radiotherapy and recovered<br/><br/>        Surgery:<br/><br/>          -  Not specified<br/>