PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent immunotherapy Chemotherapy: At least 3 weeks since prior chemotherapy and recovered No more than 1 prior chemotherapy regimen for advanced or recurrent malignancies (not including adjuvant chemotherapy) No prior nitrosoureas or intravenous mitomycin No concurrent cytotoxic chemotherapy Endocrine therapy: At least 1 week since prior hormone therapy and recovered Concurrent corticosteroid therapy allowed Radiotherapy: At least 3 weeks since prior radiotherapy and recovered Radiotherapy allowed to no more than 1 site in the thoracic or lumbar spine or pelvis Concurrent radiotherapy to a symptomatic lesion allowed after the first course of study treatment Surgery: At least 3 weeks since prior surgery and recovered (excluding recent biopsy or placement of an intravenous access device)