6Phytoestrogens and diseases of the prostate gland

Abstract

Both benign hyperplasia (BPH) and cancer of the prostate are manifest in men beyond the age of 50. Approximately 50% of men greater than 50 years of age will suffer from the symptoms associated with BPH, especially from bladder outlet obstruction. With the ever-increasing proportion of the population over 65 years of age worldwide, BPH is becoming an important medical problem as the world moves into the next millennium. Cancer of the prostate is the second most commonly diagnosed cancer after skin cancer in the male population of the United States, and the second most common cause of death from cancer after that of the lung. Overall, around the world the incidence of carcinoma of the prostate is increasing annually by 2–3%.

Both race and geographical location have a profound influence of the prevalence of prostate cancer worldwide. Black men in the USA have the highest incidence, while the incidence is much lower in Asian men from China, Japan and Thailand. Although the prostate gland is androgen-dependent, it is now recognized that the biological actions of endocrine-related factors, such as androgens, oestrogens, glucocorticoids and certain dietary and environmental factors, are mediated within the gland by various growth regulatory factors. The growth regulatory factors such as epidermal growth factor (EGF), keratinocyte growth factors (KGF), fibroblast growth factors (FGFs) and insulin-like growth factors II and I are mitogenic and directly stimulate cell proliferation under the modulating influence of steroid hormones. Steroids are therefore essential but not directly responsible for cell proliferation. Certain plant compounds such as isoflavonoids, flavonoids and lignans have been proposed as cancer protective compounds in populations with low incidences of prostate diseases. In particular, soya contains the isoflavone genistein, a compound with many properties which could influence both endocrine and growth factor signalling pathways.