Gonadotropin-releasing hormone agonists in the treatment of prostate cancer

Abstract

In 1979, the first prostate cancer patient was treated with a GnRH agonist at the Laval University Medical Center in Quebec City, Canada, thus rapidly leading to the worldwide replacement of surgical castration and high doses of estrogens. The discovery of medical castration with GnRH agonists was soon followed by fundamental changes in the endocrine therapy of prostate cancer. Most importantly, the excellent tolerance accompanying the treatment with GnRH agonists has been a key factor that permitted a series of studies demonstrating a major reduction in the death rate from prostate cancer ranging from 31 to 87% at 5 yr of follow-up in patients with localized or locally advanced prostate cancer. In fact, a one third reduction in prostate cancer deaths has been calculated in the metaanalysis of all available studies. The general acceptance of this discovery by patients and physicians is illustrated by world sales above 3.0 billion U.S. dollars in 2003. Although extremely efficient in achieving complete medical castration and well tolerated, with no other side effects than the expected hypoandrogenicity, GnRH agonists should not be administered alone. In fact, shortly after discovery of the castration effects of GnRH agonists, we observed that approximately 50% of androgens remain in the prostate after castration, thus leading to the recognition of the role of adrenal dehydroepiandrosterone as an important source of the androgens synthesized locally in the prostate and in many peripheral target tissues. We therefore developed combined androgen blockade (CAB), whereby the androgens of both testicular and adrenal origins are blocked simultaneously at start of treatment with the combination of a GnRH agonist to block the testis and a pure antiandrogen to block the action of the androgens produced locally. CAB, first used in advanced metastatic disease, has been the first treatment shown to prolong life in prostate cancer. Most interestingly, in 2002, we made the observation that CAB alone given continuously for 6.5 yr or more leads to cure of the disease in at least 90% of cases, thus suggesting that androgen blockade combining a GnRH agonist and a pure antiandrogen could well be the most efficient treatment of localized prostate cancer, and thus offering the possibility of practically eliminating death from prostate cancer.