Calcitriol and Dexamethasone in Treating Patients With Prostate Cancer Who Have Undergone Surgery or Radiation Therapy

DISEASE CHARACTERISTICS:

* Histologically confirmed adenocarcinoma of the prostate meeting all of the following criteria:

  * Curatively treated with radical prostatectomy OR definitive radiotherapy
  * No signs of clinical recurrence or dissemination of prostate cancer by digital rectal examination without tumor
  * No local recurrence by CT scan or MRI of the pelvis
  * No metastases by bone scan and chest x-ray NOTE: Prior Prostascint scans allowed regardless of results
* At least 3 prostate-specific antigen (PSA) measurements obtained over at least 90 days after radical prostatectomy on post-radiotherapy PSA nadir must be available

  * PSA at least 2 ng/mL after prostatectomy OR at least 4 ng/mL after prior radiotherapy
  * Patients previously treated with radiotherapy must have a PSA clearly rising from lowest value within 6 months after completion of therapy

PATIENT CHARACTERISTICS:

Age

* 18 and over

Performance status

* ECOG 0-1

Life expectancy

* At least 12 months

Hematopoietic

* Platelet count at least 100,000/mm\^3
* Hemoglobin at least 10 g/dL

Hepatic

* Bilirubin no greater than upper limit of normal (ULN)
* Alkaline phosphatase no greater than 2 times ULN

Renal

* Creatinine less than 1.8 mg/dL
* Phosphorus normal
* No hypercalcemia (albumin-corrected calcium greater than ULN)
* No nephrolithiasis

  * Single episode of renal lithiasis allowed provided episode occurred more than 5 years prior to study

Other

* Fertile patients must use effective double-barrier contraception for at least 1 week before, during, and for at least 2 weeks after study
* No symptomatic pancreatitis
* No uncontrolled diabetes
* No known or suspected inability to comply with study requirements (e.g., abuse of alcohol/drugs or psychotic states)
* Curatively treated condition associated with renal stones (e.g., hyperparathyroidism, bladder dysfunction, or obstructive uropathy) allowed provided patient has been free of stone formation for more than 5 years

PRIOR CONCURRENT THERAPY:

Biologic therapy

* Not specified

Chemotherapy

* No prior chemotherapy for prostate cancer
* At least 24 months since prior chemotherapy for other diseases

Endocrine therapy

* More than 6 months since prior hormonal therapy, including neoadjuvant or adjuvant androgen deprivation therapy (e.g., luteinizing hormone-releasing hormone analogue or antiandrogen)
* No prior androgen deprivation therapy of more than 8 months duration
* No prior hormonal therapy for prostate cancer more than 3 months after definitive local therapy
* No concurrent androgen therapy

Radiotherapy

* See Disease Characteristics
* More than 3 months since prior radiotherapy for locally recurrent prostate cancer
* No concurrent radiotherapy, including for pain control

Surgery

* See Disease Characteristics

Other

* More than 4 weeks since prior investigational drugs
* No concurrent medication known to affect systemic calcium metabolism, including any of the following:

  * More than 400 IU of cholecalciferol supplements
  * More than 500 IU of vitamin A supplements
  * Calcium supplements
  * Fluoride
  * Antiepileptics