soy protein in preventing recurrent cancer in patients who have undergone surgery for stage ii prostate cancer

Conditions: Prostate Cancer

Summary: 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.

objectives: * 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.

Eligibility criteria:
disease characteristics: * 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 patient characteristics: * 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 prior concurrent therapy: * see disease characteristics * no concurrent radiotherapy or hormonal therapy * no other concurrent adjuvant therapy for prostate cancer

Keywords: stage iib prostate cancer stage iia prostate cancer