PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Prior chemotherapy allowed (at least 2 weeks since prior vincristine, 3 weeks since prior procarbazine, and 6 weeks since prior nitrosoureas) and recovered Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics At least 4 weeks since prior radiotherapy Surgery: See Disease Characteristics Other: No prior or concurrent anticoagulants