DISEASE CHARACTERISTICS: Histologically confirmed prostate cancer High risk as defined by any 2 of the following: Karnofsky performance status of 70-80% Lactate dehydrogenase greater than 200 U/mL Hemoglobin less than 13 g/dL Prostate-specific antigen (PSA) at least 4 ng/mL Progressive disease based on any 1 of the following: Rise in PSA level of at least 25% above baseline At least 3 determinations taken at weekly intervals OR At least 2 determinations taken at monthly intervals New or progressive soft tissue masses on MRI or CT scan Radionucleotide bone scan with new metastatic lesion(s) Serum testosterone no greater than 30 ng/mL If no prior surgical orchiectomy, castrate levels of serum testosterone must be maintained with continuation of gonadotropin releasing hormone analogs If receiving an anti-androgen, must show progression of disease after stopping anti-androgen therapy

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: See Disease Characteristics Karnofsky 70-100% Life expectancy: Not specified Hematopoietic: See Disease Characteristics WBC at least 3,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin normal SGOT/SGPT no greater than 1.5 times upper limit of normal (ULN) Renal: Creatinine no greater than 1.5 times ULN Cardiovascular: No significant cardiovascular disease No New York Heart Association class III or IV heart disease No active angina pectoris No myocardial infarction within the last 6 months Ejection fraction at least 45% by echocardiogram or MUGA No prior hemorrhagic or thrombotic cerebral vascular accident No deep venous thrombosis Pulmonary: No pulmonary embolism within the past 6 months Other: No history of bleeding disorder or gastrointestinal bleeding that would preclude anticoagulation with warfarin No other concurrent malignancy except non-melanoma skin cancer or any curatively treated malignancy considered to be at less than 30% risk of relapse No severe infection No severe malnutrition No other serious medical illness that would preclude study

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No more than 1 prior chemotherapy regimen Endocrine therapy: See Disease Characteristics Radiotherapy: No more than 1 prior course of palliative radiotherapy No more than 1 prior radioisotope therapy with strontium chloride Sr 89 or samarium Sm 153 lexidronam pentasodium Surgery: See Disease Characteristics At least 4 weeks since prior major surgery