DISEASE CHARACTERISTICS: Histologically confirmed stage IV adenocarcinoma of the prostate Failure on standard hormone therapy Measurable disease with any PSA Accurately measured in at least 1 dimension as at least 20 mm by physical exam for clinically palpable lymph nodes and superficial skin lesions or chest x-ray for clearly defined lung lesions surrounded by aerated lung OR those lesions measured as at least 10 mm by spiral CT scan OR Nonmeasurable disease with PSA at least 5 ng/mL Nontarget lesions including small lesions with longest diameter less than 20 mm by conventional techniques or less than 10 mm by spiral CT scan and truly nonmeasurable lesions including: Bone lesions Pleural or pericardial effusions Ascites CNS lesions Leptomeningeal disease Irradiated lesions unless progression documented after radiotherapy Documented progressive systemic disease despite at least 1 endocrine manipulation with either orchiectomy or LHRH agonist (which must be continued), or diethylstilbestrol For measurable disease: Objective evidence of increase of greater than 20% in the sum of the longest diameters of target lesions from the time of maximal regression or the appearance of 1 or more new lesions For nonmeasurable disease: If bone only disease, appearance of 1 new lesion on bone scan attributable to prostate cancer along with a PSA of at least 5 ng/mL OR An elevated PSA (at least 5 ng/mL) that has risen serially from baseline on 2 occasions each at least 1 week apart Testosterone no greater than 50 ng/mL if no prior bilateral orchiectomy