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Soy Protein in Preventing Recurrent Cancer in Patients Who Have Undergone Surgery for Stage II Prostate Cancer

This study has been completed.
National Cancer Institute (NCI)
Information provided by:
National Cancer Institute (NCI) Identifier:
First received: October 2, 2008
Last updated: September 19, 2013
Last verified: August 2009

RATIONALE: Soy protein may help prevent prostate cancer recurrence in patients who have undergone surgery for prostate cancer.

PURPOSE: This randomized phase II/III trial is studying how well soy protein works and compares it to a placebo in preventing recurrent cancer in patients who have undergone surgery for stage II prostate cancer.

Condition Intervention Phase
Prostate Cancer
Dietary Supplement: soy protein isolate
Other: placebo
Phase 2
Phase 3

Study Type: Interventional
Study Design: Allocation: Randomized
Masking: Double-Blind
Primary Purpose: Treatment
Official Title: Randomized Placebo-Controlled Adjuvant Study of Prevention of Prostate Cancer Recurrence After Radical Prostatectomy by Soy Protein Isolate

Resource links provided by NLM:

Further study details as provided by National Cancer Institute (NCI):

Primary Outcome Measures:
  • Two-year PSA failure rate (as surrogate for recurrence)
  • Time to PSA failure

Secondary Outcome Measures:
  • Isoflavone uptake or compliance as measured by serum isoflavone concentration
  • Serum total cholesterol levels
  • Steroid hormone axis as measured by serum testosterone, estradiol, and SHBG levels
  • Thyroid activity as measured by serum T3 and T4 levels
  • Apoptotic activity as measured by serum soluble Fas and Fas-ligand levels
  • Angiogenesis as measured by serum VEGF and bFGF levels
  • Oxidative stress as measured by serum 8-isoprostane levels
  • IGF axis as measured by serum IGF-1 and IGFBP-3 levels
  • Equol production as measured by serum equol concentration

Estimated Enrollment: 284
Study Start Date: December 2006
Study Completion Date: July 2013
Primary Completion Date: September 2011 (Final data collection date for primary outcome measure)
Arms Assigned Interventions
Experimental: Arm I
Patients receive an oral soy protein isolate beverage once daily.
Dietary Supplement: soy protein isolate
Given orally
Placebo Comparator: Arm II
Patients receive an oral casein placebo beverage once daily.
Other: placebo
Given orally

Detailed Description:


  • Determine whether soy protein isolate reduces the PSA failure rate and time to PSA failure within 2 years following radical prostatectomy in patients who are at high risk for prostate cancer recurrence.
  • Determine the effects of soy protein isolate on intermediate biomarkers of steroid hormone axis (testosterone, estradiol, and SHBG) and thyroid activity (T3 and T4).
  • Determine the effects of soy protein isolate on intermediate biomarkers of apoptosis (soluble Fas and Fas-ligand), angiogenesis (VEGF and bFGF), antioxidant activity (8-isoprostanes), and IGF axis (IGF-1 and IGFBP-3).
  • Compare patients who are equol producers to those who are non-producers.

OUTLINE: This is a multicenter study. Patients are stratified according to hospital/clinic site (NYU vs UIC or Jesse Brown VA Medical Center vs other sites), number of high-risk characteristics (1 vs > 1), and race (African American vs non-African American [i.e., non-Hispanic White, Hispanic, Asian, and other]). Patients are randomized to 1 of 2 treatment arms.

  • Arm I: Patients receive an oral soy protein isolate beverage once daily.
  • Arm II: Patients receive an oral casein placebo beverage once daily. Treatment in both arms continues for up to 2 years in the absence of disease progression or unacceptable toxicity.

Blood samples are collected periodically for biomarker laboratory studies. Samples are analyzed to measure PSA levels by Tosoh PSA assay; cholesterol levels; isoflavone and equol concentrations by HPLC and ESA; and indicators of steroid hormone axis (testosterone, estradiol, and SHBG), indicators of thyroid activity (T3 and T4), indicators of apoptosis (soluble Fas and Fas-ligand), indicators of angiogenesis (VEGF and bFGF), indicators of oxidative stress (8-isoprostanes), and indicators of IGF axis (IGF-1 and IGFBP-3) by ELISA.


Ages Eligible for Study:   40 Years to 75 Years   (Adult, Senior)
Sexes Eligible for Study:   Male
Accepts Healthy Volunteers:   No


  • Diagnosis of prostate cancer

    • Clinically localized (T1c or T2) disease
  • At high risk for recurrence, as defined by ≥ 1 of the following:

    • Preoperative PSA > 20.0 ng/mL
    • Seminal vesicle invasion
    • Extracapsular extension (excluding the bladder neck)
    • Positive surgical margins (excluding apical margins)
    • Micrometastases in any removed pelvic lymph nodes
    • Final Gleason score of ≥ 8
  • Must have undergone radical prostatectomy for prostate cancer within the past 4 months
  • Must have an undetectable PSA (< 0.07 ng/mL) at baseline, as measured by Tosoh PSA assay
  • No clinical evidence of locally recurrent or metastatic disease


  • No significant intake of soy (i.e., more than once a week) at baseline including, but not limited to, any of the following:

    • Vegetarians who regularly consume soy products (e.g., tofu)
    • Individuals with customary Asian dietary habits, including regular intake of soy products
    • Individuals who use soy-based milk replacements
  • No anemia, iron deficiency problems, or subclinical iron deficiency at baseline
  • No diabetes
  • No thyroid disease
  • No requirement for a sodium-free diet
  • No substantive tendency to be constipated (i.e., ≥ grade 2 constipation experienced regularly)
  • No medical problem that would preclude the consumption of the soy containing beverage powder, including allergies against soy (or milk protein)
  • No concurrent major disease, including major mental disease or major substance abuse problems
  • No significant side effects from medication


  • See Disease Characteristics
  • No concurrent radiotherapy or hormonal therapy
  • No other concurrent adjuvant therapy for prostate cancer
  Contacts and Locations
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Please refer to this study by its identifier: NCT00765479

United States, Illinois
University of Illinois Cancer Center
Chicago, Illinois, United States, 60612-7243
Sponsors and Collaborators
University of Illinois at Chicago
National Cancer Institute (NCI)
Principal Investigator: Maarten C. Bosland, DVSc, PhD University of Illinois at Chicago
OverallOfficial: Roohollah Sharifi, MD University of Illinois at Chicago
  More Information

Publications automatically indexed to this study by Identifier (NCT Number): Identifier: NCT00765479     History of Changes
Other Study ID Numbers: CDR0000615902
Study First Received: October 2, 2008
Last Updated: September 19, 2013

Keywords provided by National Cancer Institute (NCI):
stage IIB prostate cancer
stage IIA prostate cancer

Additional relevant MeSH terms:
Prostatic Neoplasms
Genital Neoplasms, Male
Urogenital Neoplasms
Neoplasms by Site
Genital Diseases, Male
Prostatic Diseases processed this record on May 25, 2017