PRIOR CONCURRENT THERAPY: Biologic therapy: Prior biologic response modifier treatment allowed At least 4 weeks since prior immunotherapy At least 4 weeks since prior biologic therapy No concurrent epoetin alfa Chemotherapy: See Disease Characteristics Prior dacarbazine allowed At least 4 weeks since prior chemotherapy No other concurrent chemotherapy Endocrine therapy: No concurrent hormonal therapy for malignancy Radiotherapy: At least 3 weeks since prior radiotherapy and recovered No prior radiotherapy to areas of measurable disease unless there is clear progression or there is measurable disease outside the area of prior radiation No concurrent radiotherapy Surgery: At least 4 weeks since prior surgery and recovered Other: No other concurrent investigational drugs