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

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.