Beyond Castration-Defining Future Directions in the Hormonal Treatment of Prostate Cancer

It is now almost 70 years since Charles Huggins described the relationship between testosterone and the prostate gland. Arguably defining one of the first targeted therapies, the reduction of testosterone to castrate levels remains unaltered as the standard of care for men with metastatic prostate cancer. The failure of castration to permanently control the growth of prostate cancer leads to a state called castration-resistant prostate cancer (CRPC). Whilst numerous mechanisms have been suggested for the emergence of castration resistance [Scher and Sawyers (J Clin Oncol 23(32):8253-8261, 2005); Chen et al. (Curr Opin Pharmacol 8(4):440-448, 2008), Pienta and Bradley (Clin Cancer Res 12(6):1665-1671, 2006); Feldman and Feldman (Nat Rev Cancer 1(1):34-45, 2001); Mostaghel and Nelson (Best Pract Res Clin Endocrinol Metab 22(2):243-258, 2008)], a greater understanding of prostate cancer biology suggests that many such cancers retain a dependency on androgens and endeavour to increase bioavailable androgens through mechanisms such as AR amplification and intracrine androgen synthesis [Mohler et al. (Clin Cancer Res 10(2):440-448, 2004); Attard et al. (Clin Cancer Res 17(7):1649-1657, 2011); Hu et al. (Expert Rev Endocrinol Metab 5(5):753-764, 2010)]. With the recent approval of abiraterone acetate (Zytiga) and the pending approval of MDV3100, this article previews the future directions in clinical development and issues that will arise with the next generation of androgen-targeted agents.