PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 4 weeks since prior chemotherapy and recovered No more than 1 prior adjuvant chemotherapy regimen No more than 1 prior chemotherapy regimen for recurrent or metastatic disease No prior irinotecan or raltitrexed At least 8 weeks since prior nitrosourea or mitomycin and recovered Endocrine therapy: Not specified Radiotherapy: At least 4 weeks since prior radiotherapy and recovered Prior radiotherapy limited to no greater than 25% of bone marrow Surgery: Not specified