RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die.

PURPOSE: Phase II trial to study the effectiveness of irinotecan in treating patients who have advanced cancer of the stomach.

OBJECTIVES: I. Evaluate the response rate, survival, and toxicity of previously untreated patients with locally advanced or metastatic gastric cancer who are treated with irinotecan (CPT-11).

OUTLINE: This is a nonrandomized study. Patients receive irinotecan (CPT-11) by IV over 90 minutes every 3 weeks. Dosage modifications are made based on toxicity. Retreatment may be delayed another 3 weeks (for a total of 6 weeks) to allow for recovery from toxic effects. Patient is taken off study if they do not recover from toxic effects, unless cause is documented to be unrelated to CPT-11. Patients with stable disease or partial response continue on treatment until disease progression or intolerable toxicity. Patients with complete response continue on treatment for another 2 courses and then are observed. Patients are followed every 3 months for 3 years or until disease progression.

DISEASE CHARACTERISTICS: Histologically confirmed advanced adenocarcinoma of the stomach or gastroesophageal junction beyond hope of surgical cure and not considered a candidate for potentially curative chemotherapy/radiation therapy Measurable or evaluable disease Tumor must be accessible for biopsy No known central nervous system metastases or carcinomatous meningitis

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: At least 12 weeks Hematopoietic: Absolute granulocyte count at least 1,500/mm3 Platelet count at least 150,000/mm3 Hemoglobin at least 9.0 mg/dL (transfusion allowed) Hepatic: Bilirubin no greater than upper limit of normal (ULN), regardless of liver involvement secondary to tumor AST no greater than 3 times ULN Renal: Creatinine no greater than 1.5 times ULN Cardiovascular: No unstable angina No uncontrolled high blood pressure No active congestive heart failure No myocardial infarction in the last 6 months No serious uncontrolled cardiac arrhythmia No New York Heart Association Class III or IV heart disease Pulmonary: No interstitial pneumonia or extensive and symptomatic interstitial fibrosis of the lung No pleural effusion or ascites, which cause respiratory compromise (at least Grade 2 dyspnea) Other: No active or uncontrolled infection No prior malignancy, except for adequately treated basal cell or squamous cell skin cancer, adequately treated noninvasive carcinomas, or other cancer from which the patient has been disease free for at least 5 years Not pregnant or nursing Adequate contraception required of all fertile patients

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy for gastric or gastroesophageal junction cancer No prior irinotecan (CPT-11) or other camptothecin Endocrine therapy: Not specified Radiotherapy: No prior abdominal or pelvic radiotherapy No prior radiotherapy to greater than 25% of bone marrow No prior radiotherapy to measurable or evaluable indicator lesions At least 4 weeks since major radiotherapy (chest radiotherapy) Surgery: At least 3 weeks since major surgery and recovered At least 2 weeks since minor surgery and recovered Other: No other concurrent investigational agents