PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics No more than 2 prior chemotherapy regimens At least 3 weeks since prior chemotherapy and recovered Endocrine therapy: No concurrent corticosteroids to control symptoms of brain and/or leptomeningeal metastases Radiotherapy: At least 4 weeks since prior radiotherapy No concurrent radiotherapy to measurable lesions Surgery: Not specified Other: No concurrent hypoglycemic agents (including insulin)