DISEASE CHARACTERISTICS:<br/><br/>          -  Histologically confirmed hormone-refractory adenocarcinoma of the prostate<br/><br/>          -  Disease progression while on prior luteinizing hormone-releasing hormone (LHRH)<br/>             analogues or after orchiectomy and antiandrogens, given concurrently or consecutively<br/><br/>          -  Disease progression is defined as PSA progression documented by increases in PSA<br/>             recorded at 2 consecutive measurements over a prior reference value<br/><br/>               -  Interval of at least 1 week between the reference value and the first of these<br/>                  two PSA increases<br/><br/>          -  Continued elevation of PSA for at least 6 weeks after discontinuation of<br/>             antiandrogens<br/><br/>          -  Last PSA value at least 5 ng/mL (Hybritech equivalent)<br/><br/>          -  Must have serum testosterone less than 50 ng/mL and must continue on LHRH agonist<br/>             therapy if no prior surgical castration<br/><br/>          -  No symptomatic brain or leptomeningeal metastatic disease<br/><br/>        PATIENT CHARACTERISTICS:<br/><br/>        Age:<br/><br/>          -  Over 18<br/><br/>        Performance status:<br/><br/>          -  ECOG 0-2<br/><br/>        Life expectancy:<br/><br/>          -  Not specified<br/><br/>        Hematopoietic:<br/><br/>          -  Neutrophil count at least 1,500/mm^3<br/><br/>          -  Platelet count at least 100,000/mm^3<br/><br/>        Hepatic:<br/><br/>          -  Bilirubin less than 1.5 times upper limit of normal (ULN)<br/><br/>          -  ALT/AST no greater than 2.5 times ULN (5 times ULN if liver metastases present)<br/><br/>        Renal:<br/><br/>          -  Creatinine no greater than 1.7 mg/dL<br/><br/>          -  No uncontrolled hypercalcemia<br/><br/>        Cardiovascular:<br/><br/>          -  No history of severe heart disease<br/><br/>          -  No myocardial infarction within the past 6 months<br/><br/>          -  No cardiac insufficiency<br/><br/>          -  Normal cardiac function by MUGA scan and 12-lead EKG<br/><br/>        Other:<br/><br/>          -  No other prior or concurrent malignancy except basal cell or squamous cell skin<br/>             cancer<br/><br/>          -  No uncontrolled systemic nonmalignant disease or infection<br/><br/>          -  No psychological, familial, or geographical conditions that would preclude compliance<br/><br/>        PRIOR CONCURRENT THERAPY:<br/><br/>        Biologic therapy:<br/><br/>          -  Not specified<br/><br/>        Chemotherapy:<br/><br/>          -  At least 4 weeks since prior chemotherapy<br/><br/>        Endocrine therapy:<br/><br/>          -  See Disease Characteristics<br/><br/>          -  No prior hormonal therapy except estramustine<br/><br/>          -  No concurrent estramustine<br/><br/>        Radiotherapy:<br/><br/>          -  At least 4 weeks since prior radiotherapy<br/><br/>          -  No concurrent radiotherapy (e.g., for painful bone metastases)<br/><br/>        Surgery:<br/><br/>          -  See Disease Characteristics<br/><br/>        Other:<br/><br/>          -  No other concurrent experimental drugs or investigational therapy<br/>