Defining the role of antiandrogens in the treatment of prostate cancer

Prostate carcinoma: defining therapeutic objectives and improving overall outcomes

The development and progression of a prostate carcinoma from prediagnosis to death can be characterized as a series of clinical states. The states are milestones that can be used to assess prognosis, define therapeutic objectives, and assess outcomes. The antitumor effects of hormone therapies and cytotoxic agents in patients with prostate carcinoma are placed in context along with the bidrectional tumor-host interactions that contribute to the growth and resistance of osseous lesions. Identifying the factors that contribute to the growth of the disease at different points in the illness has lead to novel, systemic approaches. Proving the benefit of these approaches requires a series of unique trials with unique endpoints relevant to the clinical state of the patients and the specific therapy under evaluation.

Clinical pharmacokinetics of the antiandrogens and their efficacy in prostate cancer

Prostatic cancer is the second most common cause of cancer death in males. Treatment by radical prostatectomy and radiotherapy is useful in the early stages of the disease. Whenever metastases occur, patients are usually treated by surgical (orchidectomy) or medical [gonadotropin releasing hormone (GnRH) analogue] castration. This form of treatment is, however, associated with unwanted adverse effects, such as flushing, loss of libido and potency and all patients ultimately escape therapy after a delay of 1 to 2 years. For this reason antiandrogens have been developed as another means of endocrine ablation therapy. Antiandrogens fall in 2 groups of which the first group, the steroidal antiandrogens such as cyproterone acetate (CPA), have a direct blocking effect at the cellular level but also inhibit testosterone production by their additional gestagenic properties blocking gonadotropin secretion. Except in preventing the flare-up associated with the start of GnRH analogue therapy and in reducing flushing, no evidence exist of any superiority for CPA over classical therapy in terms of adverse effects and survival. The second group, the nonsteroidal or 'pure' antiandrogens, only block androgens at the cellular level without any central effects. In contrast with other forms of castration, patients on pure antiandrogens as monotherapy preserve their sexual function and potency, at the expense of a slightly inferior androgen blockade and gynecomastia. These latter effects are explained by a compensatory rise in androgens as a result of the blockade at the central level, which weakens the androgen blockade, and by peripheral aromatisation of the increased androgens to oestrogens. In addition, some evidence exist that pure antiandrogens improve survival if combined with other forms of castration as they also inhibit the adrenal androgens, the so-called maximal androgen blockade (MAB). If patients escape control under MAB, a trial of stopping the antiandrogen must always be considered, as some tumours have 'learned' to be activated by these drugs. At the moment it is not yet clear if antiandrogens are of any benefit in downstaging the extent of disease before prostatectomy and/or radiotherapy. Of the currently known pure antiandrogens, bicalutamide offers some advantages over flutamide as it possesses a much longer half-life, allowing a once daily regimen, and has advantages over nilutamide in terms of fewer adverse effects.