DISEASE CHARACTERISTICS: Histologically proven adenocarcinoma of the prostate that is chemotherapy naive and refractory to hormonal therapy with combined androgen blockade No concurrent antiandrogen therapy withdrawal: Must continue antiandrogen therapy until completion of study OR Must discontinue flutamide at least 4 weeks before or bicalutamide at least 8 weeks before study enrollment, and must have disease progression off antiandrogen therapy, defined by serial increase in PSA (at least 2 measurements taken at least 2 weeks apart) or measurable tumor Concurrent LHRH antagonist allowed if no prior orchiectomy No minimum PSA level required Measurable or evaluable disease An increase in PSA or pain without measurable or evaluable disease does not constitute hormone refractory disease