• Response of serum PSA [ Designated as safety issue: No ]
  

• Changes in PSA slope [ Designated as safety issue: No ]
  
• Changes in PSA doubling time [ Designated as safety issue: No ]
  
• Toxicity as assessed by NCI CTCAE v3.0 [ Designated as safety issue: Yes ]
  
• Time to progression [ Designated as safety issue: No ]
  
• Correlation of cholecalciferol and soy isoflavones with vitamin D receptor signaling and p21 and p27 expression in peripheral blood lymphocytes as assessed by immunoblot analysis of cell lysates and quantitative PCR [ Designated as safety issue: No ]
  

OBJECTIVES:

• Test the response of biochemically recurrent prostate cancer to a combination of cholecalciferol (i.e., vitamin D) and soy isoflavones (i.e., soy extract) after failed definitive local therapy as determined by PSA response.

OUTLINE: Patients receive oral cholecalciferol twice daily and a soy supplement (i.e., soy bar or shake) once daily. Treatment continues for 3-12 months in the absence of disease progression or unacceptable toxicity.

Blood samples are obtained at baseline and periodically during study to measure serum PSA, serum calcium, plasma cholecalciferol, and plasma soy isoflavone levels. Blood samples are also analyzed for expression of cholecalciferol receptor, p21, and p27 in peripheral blood lymphocytes as surrogate markers of the actions of cholecalciferol and genistein. Protein expression is assessed by immunoblot analysis of cell lysates as well as quantitative polymerase chain reaction.

Patients complete a toxicity questionnaire once each month to assess for cholecalciferol and soy supplementation toxicities and symptoms of hypercalcemia.

After completion of study therapy, patients are followed every 3 months for 1 year.

DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the prostate

  • No evidence of metastatic disease by bone scan or CT scan

• Biochemical-only relapse after failed radical prostatectomy, brachytherapy, or external beam radiotherapy

  • Meets American Society for Therapeutic Radiology and Oncology definition of biochemical relapse as 3 consecutive rising PSA levels obtained at least 1 month apart
  • PSA doubling time of ≥ 6 months, as demonstrated by 3 PSA measurements obtained ≥ 2 months apart

• Minimum PSA ≥ 1.5 ng/mL

  • Bone scan and CT scan required for PSA ≥ 10 ng/ mL
• Testosterone ≥ 150 ng/dL
• No clinically evident brain metastases

PATIENT CHARACTERISTICS:

• ECOG performance status 0-2
• Life expectancy > 3 months
• Absolute granulocyte count ≥ 1,000/mm³
• Platelet count ≥ 100,000/mm³
• Hemoglobin ≥ 9.0 g/dL
• Creatinine ≤ 2.0 mg/dL
• Total bilirubin ≤ 2.0 mg/dL
• Calcium > 8.5 mg/dL and < 10.5 mg/dL
• No serious medical illness that would limit survival to < 3 months, or psychiatric condition that would preclude giving informed consent
• No other malignancy except nonmelanoma skin cancer, adequately treated stage I or II cancer from which the patient is currently in complete remission, or any other cancer from which the patient has been disease-free for the past 5 years
• No active, uncontrolled bacterial, viral, or fungal infection
• No hemorrhagic disorder
• No history of hypercalcemia

PRIOR CONCURRENT THERAPY:

• More than 6 months since prior hormonal therapy
• At least 2 years since prior definitive radiotherapy
• More than 1 year since prior phytotherapeutics, including PC-SPES and saw palmetto
• More than 3 months since prior soy, cholecalciferol (> 400 IU per day), calcium, fish oil, or multivitamin supplements
• No concurrent cholecalciferol, calcium, or soy supplements
• No concurrent chemotherapy with nonstudy drugs