Calcitriol and Dexamethasone in Treating Patients With Prostate Cancer That Did Not Respond to Hormone Therapy

DISEASE CHARACTERISTICS: * History of androgen-independent prostate cancer * Evidence of rising PSA level (with or without new lesion by radiograph or physical examination), defined as follows: * PSA level \> 5 ng/mL and clearly rising on 2 measurements taken ≥ 2 weeks apart after androgen deprivation therapy (i.e., orchiectomy or luteinizing hormone-releasing hormone \[LHRH\] analogue) and antiandrogen withdrawal, if appropriate * PSA rising before and on the first value taken at 4 or 6 weeks after antiandrogen cessation is considered disease progression * Measurable or evaluable disease as defined by any of the following: * Measurable or evaluable tumor masses by radiograph or physical examination * Evaluable PSA * Concurrent LHRH analogue or diethylstilbestrol (DES) for testicular androgen suppression required if no prior bilateral orchiectomy * Patients receiving other monotherapy for testicular androgen suppression must switch to a LHRH analogue or DES ≥ 14 days prior to study entry PATIENT CHARACTERISTICS: * ECOG 0-2 * Life expectancy ≥ 12 weeks * ANC ≥ 1,000/mm³ * Platelet count ≥ 75,000/mm³ * Hemoglobin \> 8.9 g/dL (transfusion or erythropoietin support allowed) * Serum creatinine ≤ 1.8 mg/dL * AST ≤ 4 times upper limit of normal (ULN) * Total bilirubin ≤ 2.0 mg/dL * Serum corrected calcium \< ULN * No history of nephrolithiasis within the past 5 years * No unstable, uncontrolled peptic ulcer disease, congestive heart failure, glaucoma, HIV, or diabetes PRIOR CONCURRENT THERAPY: * At least 28 days since prior androgen deprivation therapy (≥ 42 days for bicalutamide) * A 28-day washout period is not required for patients who have previously progressed despite antiandrogen withdrawal and who have resumed antiandrogens without reduction of PSA * At least 14 days since prior radiotherapy * At least 28 days since prior strontium 89 * At least 28 days since prior chemotherapy and/or investigational agents * No concurrent medications or supplements that contain additional calcium (e.g., Tums) * No concurrent radiotherapy for pain control or any other indication * Concurrent bisphosphonates allowed provided dose/regimen is stable