DISEASE CHARACTERISTICS: Histologically confirmed metastatic or recurrent adenocarcinoma of the stomach or gastroesophageal junction Bidimensionally measurable or evaluable disease Mediastinal or hilar lymph nodes assessed by CT or MRI scan must be at least 2 cm in diameter to be considered measurable Must not be curable with a combination of chemotherapy and radiotherapy No brain metastases No osseous metastasis as only site of disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: At least 12 weeks Hematopoietic: Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 mg/dL SGOT no greater than 3 times upper limit of normal No known Gilbert's syndrome Renal: Creatinine no greater than 1.5 mg/dL Calcium no greater than 12 mg/dL No symptomatic hypercalcemia under treatment Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No history of seizures No serious concurrent infections or nonmalignant medical illnesses that are uncontrolled or whose control may be jeopardized by study complications No psychiatric disorders that would preclude study compliance No other active malignancy within the past 5 years except nonmelanoma skin cancer or carcinoma in situ of the cervix No uncontrolled diabetes mellitus (i.e., random blood sugar less than 250 mg)

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior immunotherapy for metastatic disease No concurrent immunotherapy Chemotherapy: See Disease Characteristics No prior chemotherapy for metastatic disease No prior radiosensitizing chemotherapy in metastatic setting At least 6 months since prior adjuvant therapy No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics At least 4 weeks since prior radiotherapy and recovered No prior radiotherapy to major bone marrow containing areas (e.g., pelvis, lumbar spine) No prior radiotherapy to only evaluable lesion No concurrent radiotherapy Surgery: At least 1 week since minor surgery and 3 weeks since major surgery and recovered Other: No concurrent phenytoin, phenobarbital, or other antiepileptic prophylaxis No concurrent prochlorperazine on day of irinotecan administration No other concurrent medications except for analgesics, chronic treatments for concurrent medical conditions, or agents required for life threatening medical problems