<br>        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>