DISEASE CHARACTERISTICS: Histologically confirmed adenocarcinoma of the prostate with progressive systemic disease despite at least 1 endocrine manipulation including 1 of the following: Orchiectomy LHRH analogue with or without flutamide, megestrol, or diethylstilbestrol Flutamide must be discontinued for at least 2 weeks with PSA stabilized above normal or rising Measurable or evaluable disease No brain metastasis