DISEASE CHARACTERISTICS: Histologically confirmed metastatic hormone-refractory adenocarcinoma of the prostate gland Elevated serum acid phosphatase or PSA levels must not be only evidence of disease Must have evidence of progressive metastatic disease (e.g., bone, pelvic mass, lymph node, liver, or lung metastases) Radiological evidence of hydronephrosis alone does not constitute evidence of metastatic disease Patients with bone metastases only (i.e., lacking measurable soft tissue disease) must have PSA level of at least 20 ng/mL Patients with soft tissue metastases and/or visceral disease must have either bidimensionally measurable disease or a PSA level of at least 20 ng/mL Must have had prior treatment with bilateral orchiectomy or other primary hormonal therapy (e.g., estrogen therapy, LHRH-blocker plus flutamide, etc.) with evidence of treatment failure No carcinomatous meningitis or brain metastases