Mitoxantrone Following Surgery in Treating Patients With Prostate Cancer at High Risk for Recurrence

DISEASE CHARACTERISTICS: Adenocarcinoma of the prostate treated by radical prostatectomy within the past 3 months Considered to be at high risk for recurrence as defined by at least 1 of the following characteristics on the radical prostatectomy specimen: Positive seminal vesicles Gleason 6 and preoperative PSA greater than 18 ng/mL Gleason 7 and preoperative PSA greater than 14 ng/mL Gleason 8, 9, or 10 and any preoperative PSA Undetectable PSA (i.e., less than 0.1 ng/mL) within 3 months following radical prostatectomy and at time of enrollment Negative lymph nodes at time of radical prostatectomy if lymphadenectomy performed Extracapsular penetration and/or positive surgical margins allowed PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Zubrod 0-1 Life expectancy: Not specified Hematopoietic: Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) SGOT no greater than 2 times ULN Renal: Not specified Cardiovascular: No New York Heart Association class III or IV cardiac disease or angina pectoris No myocardial infarction within the past 6 months PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent filgrastim or sargramostim except for febrile neutropenia Chemotherapy: No other concurrent chemotherapy Endocrine therapy: No prior neoadjuvant or adjuvant hormonal therapy for prostate cancer No concurrent hormonal therapy except for non-disease related conditions (e.g., insulin for diabetes) No concurrent systemic corticosteriods unless for adrenal insufficiency No concurrent prednisone, dexamethasone, or other steroidal antiemetics At least 6 months since prior finasteride No concurrent finasteride No concurrent antiandrogens (e.g., flutamide, bicalutamide, nilutamide) or gonadotropin releasing hormone agonists (e.g., leuprolide, goserelin) Radiotherapy: No prior adjuvant radiotherapy for prostate cancer No prior pelvic radiotherapy for prostate cancer Surgery: See Disease Characteristics Other: At least 6 months since prior saw palmetto No concurrent compounds with 5 alpha-reductase inhibitor activity (e.g., saw palmetto)