Calcitriol Plus Dexamethasone in Treating Patients With Prostate Cancer That Has Not Responded to Hormone Therapy

DISEASE CHARACTERISTICS: * Histologically confirmed adenocarcinoma of the prostate with progressing regional or metastatic disease despite primary hormonal therapy (bilateral orchiectomy, estrogen, or luteinizing hormone-releasing hormone (LHRH) therapy with or without simultaneous antiandrogen) * Documented new lesions or rising PSA (at least 50% increase on 3 measurements more than 2 weeks apart) after prior antiandrogen or progestational agent, or other hormonal agent cessation PATIENT CHARACTERISTICS: Age: * 18 and over Performance status: * ECOG 0-2 Life expectancy: * Not specified Hematopoietic: * WBC greater than 3,500/mm\^3 * Absolute neutrophil count greater than 1,500/mm\^3 * Platelet count greater than 100,000/mm\^3 Hepatic: * Bilirubin less than 2.0 mg/dL * SGOT less than 4 times upper limit of normal Renal: * Creatinine no greater than 1.8 mg/dL Other: * No uncontrolled diabetes mellitus * Fertile patients must use effective double barrier contraception for at least 1 week before, during, and at least 2 weeks after study participation PRIOR CONCURRENT THERAPY: Biologic therapy: * Concurrent epoetin alfa for anemia allowed Chemotherapy: * Not specified Endocrine therapy: * See Disease Characteristics * At least 28 days since prior antiandrogens or progestational agents * Concurrent testicular androgen suppression with an LHRH analog (leuprolide or goserelin) allowed in non-orchidectomized patients Radiotherapy: * No concurrent radiotherapy Surgery: * Not specified Other: * No concurrent bisphosphonates