The gonadotropin-releasing hormone antagonist abarelix depot versus luteinizing hormone releasing hormone agonists leuprolide or goserelin: Initial results of endocrinological and biochemical efficacies in patients with prostate cancer

Purpose: We contrasted the endocrinological and biochemical efficacies of a barelix depot, a pure gonadotropin-releasing hormone antagonist, with a pro spective concurrent control cohort receiving luteinizing hormone releasing hormone (LH-RH) agonists with or without antiandrogen for treatment of pati ents with prostate cancer receiving initial hormonal therapy. Materials and Methods: In this phase 2 open label study 242 patients with p rostate cancer requiring initial hormonal treatment received abarelix depot (209) or LH-RH agonists (33) with or without antiandrogen. A total of 100 mg. abarelix depot was delivered intramuscularly every 28 days with an addi tional injection on day 15. LH-RH agonists with or without antiandrogen wer e administered according to the depot formulation used. Endocrine efficacy was measured by the absence of testosterone surge and rapidity of castratio n onset. The rate of prostate specific antigen decrease was assessed. Results: No patient treated with abarelix depot had testosterone surge duri ng week 1 compared with 82% of those treated with LH-RH agonists. The conco mitant administration of antiandrogen had no effect. During the first week of drug administration, in 75% of patients treated with abarelix depot and in 0% of those treated with LH-RH agonist medical castration was achieved. Prostate specific antigen decrease was faster, with no flare or surge in pa tients treated with abarelix depot. Abarelix depot was well tolerated. Conclusions: Abarelix depot represents a new class of hormonal therapy, gon adotropin releasing hormone antagonists, that has rapid medical castration and avoids the testosterone surge characteristic of LH-RH agonists.