PRIOR CONCURRENT THERAPY: Biologic therapy: One prior biologic therapy allowed Chemotherapy: See Disease Characteristics No more than one prior chemotherapy for metastatic disease or adjuvant treatment At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered Endocrine therapy: No concurrent oral hypoglycemics or insulin Radiotherapy: At least 4 weeks since prior radiotherapy and recovered Surgery: Not specified Other: No other concurrent investigational agents No concurrent combination antiretroviral treatment for HIV