DISEASE CHARACTERISTICS: Histologically proven advanced malignancies that are sensitive to cyclophosphamide/carboplatin therapy OR refractory to standard therapy, including, but not limited to: Ovarian epithelial cancer Colorectal cancer Breast cancer Sarcoma Non-small cell lung cancer Malignant melanoma Upper gastrointestinal cancers Small cell lung cancer

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 SWOG 0-2 Life expectancy: At least 3 months Hematopoietic: WBC at least 3,500/mm3 Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 8.5 g/dL Hepatic: Bilirubin no greater than 1.5 mg/dL Renal: Creatinine no greater than 1.5 mg/dL OR Creatinine clearance at least 60 mL/min OR Iothalamate clearance at least 60 mL/min Cardiovascular: No significant coronary artery disease (angina of New York Heart Association class 3 or greater) Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No psychosis

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)