PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 6 weeks since antineoplastic chemotherapy unless unequivocal tumor progression Endocrine therapy: Concurrent corticosteroids allowed at lowest possible dose and stable for at least 10 days prior to entry Radiotherapy: At least 3 months since radiotherapy to site of measurable disease within the nervous system unless unequivocal tumor progression Surgery: See Disease Characteristics