DISEASE CHARACTERISTICS: Histologically or cytologically confirmed metastatic hormone refractory prostate cancer Disease progression after orchiectomy or during hormonal therapy Measurable or evaluable disease At least 2 consecutive increases in PSA At least 1 week between reference value and first increase OR Third value must be higher than second if second value is less than reference value PSA at least 5 ng/mL No leptomeningeal or brain metastases

PATIENT CHARACTERISTICS: Age: 18 to 85 Performance status: WHO 0-2 Life expectancy: Not specified Hematopoietic: WBC at least 3,500/mm3 OR Granulocyte count at least 2,000/mm3 Hemoglobin at least 9.0 g/dL Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) SGOT no greater than 2.5 times ULN Renal: Creatinine no greater than 1.5 times ULN Other: No other prior malignancies in past 5 years except curatively treated basal cell or squamous cell carcinoma of the skin No other significant disease that would preclude study No concurrent active severe infections

PRIOR CONCURRENT THERAPY: Biologic therapy: Prior gene therapy and antibody therapy allowed Chemotherapy: No prior cytostatic chemotherapy, including estramustine Endocrine therapy: See Disease Characteristics At least 1 month since prior antiandrogen therapy (e.g., flutamide or bicalutamide) without tumor response OR Concurrent antiandrogen therapy allowed if clinically unacceptable to discontinue use If disease progressed while receiving hormonal agents (e.g., goserelin, leuprolide, diethylstilbestrol), therapy must continue during study Radiotherapy: At least 4 weeks since prior radiotherapy No prior radiotherapy to lesions to be evaluated No concurrent radiotherapy to more than one area Surgery: See Disease Characteristics Other: Prior noncytostatic therapy allowed At least 1 month since prior investigational drugs