DISEASE CHARACTERISTICS: Histologically proven adenocarcinoma of the prostate with evidence of bone, pelvic, lymph node, liver, or lung metastases Radiologic evidence of hydronephrosis alone does not constitute evidence of metastatic disease Patients with bone metastases only (i.e., no measurable soft tissue disease) must have PSA level of at least 5 ng/mL Prior bilateral orchiectomy or other prior primary hormonal therapy (e.g., estrogen therapy, LHRH agonist with or without flutamide or bicalutamide) with evidence of treatment failure Patients without prior orchiectomy must continue on LHRH agonist therapy At least 4 weeks since prior flutamide (at least 6 weeks since prior bicalutamide or nilutamide) with continued evidence of progressive disease (i.e., increasing PSA) Must have evidence of progressive disease, defined by any one or more of the following after completion of primary hormonal therapy (which must include either orchiectomy or LHRH agonist therapy): Rising PSA, defined by at least 50% increase above nadir value achieved on prior therapy Increase confirmed by a second measurement obtained a minimum of 1 week following the index measurement, and confirmed by a third measurement if the second value is less than the first increase One of more new bone metastases on radionuclide bone scan or x-ray film New or enlarging soft tissue metastases Disease related symptoms such as pain not required Ineligible if an elevated serum acid phosphatase or PSA level is the only evidence of disease No history of brain metastases or carcinomatous meningitis