Prostate cancer (PC) is the most frequently occurring cancer in men. Its clinical incidence and mortality rates vary geographically, being much lower in Asia than in Western countries. Notably, latent PCs seem to be equally distributed, thus supporting the hypothesis, that environmental factors may be important in prostate cancer progression. Moreover, epidemiological evidence strongly supports the concept that the incidence of clinical prostate cancer depends on lifestyle factors, mainly related to diet. The isoflavone genistein and the flavonoid quercetin have been identified as likely preventive candidates. The aim of the intended clinical trial is to evaluate the hypothesized effectiveness of polyphenolic phytochemicals with highly purified dietary supplements in patients at high risk of clinical PC and without systemic treatment. This will provide data, which serve as an important pre-requesite for targeted dietary interventions using alternative medicine as preventive measures in men with latent PC.