Nutritional Supplement with Fermented Soy in Patients Under Active Surveillance for Low-Risk or Intermediate-Risk Prostate Cancer: Results from the PRAEMUNE Trial

<i>Background/Objectives:</i> To investigate the effect of a fermented soy supplement during 18 months in patients under active surveillance (AS) for low-risk and selected favorable intermediate-risk prostate cancer (PCa), with an emphasis on PSA modulation. <i>Methods:</i> Low-risk patients with ISUP grade 1, clinical stage cT1 or cT2a, PSA < 10 ng/mL and favorable intermediate-risk patients with ISUP grade 2 (<10% pattern 4), clinical stage T2b-c, PSA 10-20 ng/mL. The primary outcome was PSA response defined as maximum PSA rise less than or equal to 0.87 ng/mL after 1 year, based on the weighted average of PSA velocity (PSAV) in previous studies in similar populations. Secondary outcomes were disease progression, adverse histology on repeat biopsy or switch to active therapy. In addition, primary and secondary outcomes with imputed data were also determined as sensitivity analyses, using Mann-Whitney U or Chi-squared tests. <i>Results:</i> Overall, 92 (61.3%) of 150 patients showed a PSA level response. This was more evident in ISUP 1 patients and resulted in fewer follow-up MRIs and fewer control biopsies, as well as a fewer number of positive control biopsies with statistical significance in the imputed dataset. Obtaining a PSA response was numerically associated with less initiated therapy. <i>Conclusions:</i> a fermented soy supplement in patients under AS for low-risk and selected favorable intermediate-risk PCa could be useful in selecting patients who may remain under AS or who may need to switch to active therapy.