RATIONALE: Calcitriol may help tumor cells develop into normal cells. Dexamethasone may increase the effectiveness of calcitriol by making tumor cells more sensitive to the drug.

PURPOSE: Phase II trial to study the effectiveness of combining calcitriol with dexamethasone in treating patients with prostate cancer who have undergone surgery or radiation therapy.

OBJECTIVES:

• Determine whether calcitriol and dexamethasone can slow the rise in prostate-specific antigen (PSA) levels in patients with early, recurrent prostate cancer after prior radical prostatectomy or radiotherapy.
• Determine the safety of this regimen in these patients.
• Determine the utility of serum PSA in monitoring the therapeutic effect of calcitriol in these patients.

OUTLINE: Patients are stratified according to prior therapy (radical prostatectomy vs radiotherapy).

Patients receive oral calcitriol once daily on days 1-3 alone on week 1. Beginning on week 3, patients receive calcitriol as in week 1 and oral dexamethasone on days 0-4. Courses repeat every 2 weeks in the absence of disease progression or unacceptable toxicity.

PROJECTED ACCRUAL: A total of 56 patients (28 per stratum) will be accrued for this study.

• Dietary Supplement: calcitriol
• Drug: dexamethasone

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