PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No greater than 3 prior chemotherapy regimens (adjuvant and metastatic) At least 3 weeks since prior adjuvant and metastatic chemotherapy (6 weeks for nitrosoureas or mitomycin and 4 weeks for carboplatin or other experimental anti cancer drugs) and recovered At least 1 year since prior high dose chemotherapy with bone marrow or stem cell support No other concurrent chemotherapy Endocrine therapy: Prior hormonal therapy allowed No concurrent hormonal therapy Radiotherapy: No prior radiotherapy to greater than 25% of bone marrow At least 4 weeks since prior radiotherapy, except for low dose myelosupressive radiotherapy, and recovered Concurrent palliative radiotherapy allowed Surgery: Not specified Other: At least 4 weeks since prior experimental drug or anticancer therapy No other concurrent investigational or anticancer therapy