Inclusion Criteria

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed adenocarcinoma of the
prostate Stage IV Evidence of progression despite standard hormonal management including
antiandrogen withdrawal, defined as 1 of the following: Development of new metastatic
lesions Increase in cancer-related pain A 50% rise in prostate-specific antigen (PSA)
levels confirmed by 2 measurements at least 2 weeks apart PSA at least 5 ng/mL
Testosterone less than 50 ng/mL

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-1 Life expectancy: At
least 3 months Hematopoietic: WBC at least 3,000/mm3 Neutrophil count at least 1,500/mm3
Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 2.0 mg/dL Renal:
Creatinine no greater than 1.3 mg/dL Calcium no greater than 10.5 mg/dL Phosphorus no
greater than 4.2 mg/dL No kidney stones within the past 5 years No history of
cancer-related hypercalcemia Cardiovascular: No uncontrolled heart failure Other: No other
malignancy within the past 5 years except nonmelanoma skin cancer No significant active
medical illness that would preclude study Fertile patients must use effective
contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No more than 1
type of prior chemotherapy for prostate cancer No prior carboplatin or cisplatin for
prostate cancer Endocrine therapy: See Disease Characteristics At least 4 weeks since
prior flutamide or nilutamide (6 weeks for bicalutamide) Concurrent primary hormonal
therapy allowed (e.g., gonadotropin-releasing hormone agonist or antagonist) Radiotherapy:
At least 1 month since prior radiotherapy At least 2 months since prior strontium chloride
Sr 89 or samarium Sm 153 lexidronam pentasodium Surgery: Concurrent orchiectomy allowed
Other: At least 7 days since prior thiazide diuretic At least 30 days since prior
investigational therapy No prior calcitriol for prostate cancer No concurrent
magnesium-containing antacids, bile-resin binders, or calcium supplements