Biology and natural history of prostate cancer and the role of chemoprevention.

Androgens not only play an important role in the development and function of the prostate but they are also intimately involved in the development and progression of prostate cancer (PCa). Within the prostate, testosterone is converted to the more potent androgen dihydrotestosterone (DHT) via the action of 5α-reductase enzymes. DHT is the primary prostatic androgen and promotes the growth and survival of normal, hyperplastic and malignant prostate tissues. Throughout the different stages of PCa [prostatic intraepithelial neoplasia (PIN), localised, recurrent, and metastatic] there is an increase in expression of 5α-reductase enzymes, particularly in localised high-grade carcinoma. Specifically inhibiting 5α-reductase may reduce the production of DHT in the prostate while maintaining other endogenous hormone levels. Clinical studies have shown significant PCa risk reduction by blocking this pathway with 5α-reductase inhibitors (5ARIs). However, this comes at a risk, albeit low, with sexual side effects, gynaecomastia and cardiac failure. In addition, one study has shown a slight, but significant, risk of high-grade PCa. The currently available evidence does not support the routine use of 5α-reductase inhibitors to prevent PCa in the general population. It could, however, be considered as an individual option for high-risk or concerned patients with appropriate education from the prescribing provider.