Vitamin D and Soy Supplements in Treating Patients With Recurrent Prostate Cancer

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.

Inclusion:

- Age > 18 years

- Histologically confirmed adenocarcinoma of the prostate

- Biochemical relapse following definitive therapy by ASTRO criteria (PSA with 3
consecutive rising measurements separated by at least one month) and minimum PSA ≥ 1.0
ng/mL

- PSA doubling time of ≥ 6 months, as demonstrated by 3 PSA measurements obtained ≥ 2
months apart

- No hormonal therapy in 6 months prior to enrollment

- ECOG performance status 0-2

- Life expectancy > 3 months

- At least 2 years since prior definitive radiotherapy

- No concurrent cholecalciferol, calcium, or soy supplements

- 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

- Testosterone ≥ 150 ng/dL

Exclusion:

- No clinically evident brain metastases

- Concurrent cholecalciferol, calcium, or soy supplements

- Concurrent chemotherapy with nonstudy drugs

- Serious medical illness that would limit survival to < 3 months, or psychiatric
condition that would preclude giving informed consent

- 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

- Active, uncontrolled bacterial, viral, or fungal infection

- Hemorrhagic disorder

- Evidence of metastatic disease by bone scan or CT scan

- History of hypercalcemia

- More History of exposure to other phytotherapeutics, including PC-SPES and Saw
Palmetto, within the last year.