PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics At least 4 weeks since chemotherapy and recovered No more than 2 different prior chemotherapy regimens for metastatic disease No prior mitomycin or nitrosourea Lifetime cumulative doxorubicin dose less than 350 mg per square meter Endocrine therapy: Not specified Radiotherapy: At least 2 weeks since radiotherapy and recovered Surgery: At least 3 weeks since major surgery and recovered