PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent immunotherapy or biologic therapy No concurrent growth factors or epoetin alfa Chemotherapy: At least 4 weeks since prior chemotherapy No more than 1 prior chemotherapy regimen for metastatic disease No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics Prior radiotherapy for local control or as palliative therapy for a painful bony lesion allowed No prior radiotherapy to 50% or more of bone marrow At least 4 weeks since prior radiotherapy to 15% or more of bone marrow (2 weeks for radiotherapy to less than 15% of bone marrow) and recovered No concurrent radiotherapy Surgery: Not specified Other: Recovered from any prior therapy No other concurrent investigational drugs