PATIENT CHARACTERISTICS: Age: 18 and over Performance status: WHO 0-2 Life expectancy: Not specified Hematopoietic: WBC at least 3,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.25 times upper limit of normal (ULN) (1.5 times ULN if liver metastasis present) AST and ALT no greater than 3 times ULN (5 times ULN if liver metastasis present) Renal: Creatinine no greater than 1.25 times ULN Cardiovascular: No severe cardiac disease No uncontrolled angina pectoris No myocardial infarction within the past 6 months Gastrointestinal: No unresolved bowel obstruction or subobstruction No uncontrolled Crohn's disease or ulcerative colitis No history of chronic diarrhea Other: No second malignancy except carcinoma in situ of the cervix or nonmelanomatous skin cancer No other uncontrolled severe medical condition Not pregnant or nursing Fertile patients must use effective contraception