PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy for metastatic cancer At least 6 months since prior adjuvant chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics No prior radiotherapy Surgery: At least 21 days since prior laparotomy or laparoscopic procedure with or without resection Other: No concurrent sorivudine or chemically related analogues (e.g., brivudine)