OUTLINE: This is a randomized, multicenter study. Patients are randomized to one of two treatment arms. Arm I: Patients receive leucovorin calcium IV over 2 hours followed by fluorouracil IV over 24 hours on days 1, 8, 15, 22, 29, and 36. Arm II: Patients receive irinotecan IV over 30 minutes followed by leucovorin calcium IV over 2 hours and fluorouracil IV over 24 hours on days 1, 8, 15, 22, 29, and 36. Treatment in both arms repeats every 7 weeks in the absence of disease progression or unacceptable toxicity. Patients in arm I who develop disease progression begin second-line therapy comprising irinotecan, fluorouracil, and leucovorin calcium within 2 months of progression. Patients with complete response are taken off study after receiving treatment for one year. Quality of life is assessed before beginning study, after completion of each course, at 4 weeks after completion of study, and then every 2 months until disease progression or death. Patients are followed every 2 months until disease progression or death.