PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No more than 2 other prior chemotherapy regimens (e.g., one frontline plus one salvage regimen) At least 2 weeks since prior chemotherapy and recovered Endocrine therapy: Not specified Radiotherapy: At least 1 month since prior radiotherapy and recovered Surgery: Not specified Other: See Disease Characteristics At least 2 weeks since other prior investigational agents and recovered No concurrent intrathecal drugs