ARTICLE ABSTRACTPurpose: Degarelix, a new gonadotropin-releasing hormone (GnRH) receptor antagonist with demonstrated efficacy as first-line treatment in the management of high-risk prostate cancer, possesses some theoretical advantages over luteinizing hormone–releasing hormone (LHRH) analogues in terms of avoiding “testosterone flare” and lower follicle-stimulating hormone (FSH) levels. We set out to determine whether preoperative degarelix influenced surrogates of disease control in a randomized phase II study.Experimental Design: Thirty-nine patients were randomly assigned to one of three different neoadjuvant arms: degarelix only, degarelix/bicalutamide, or LHRH agonist/bicalutamide. Treatments were given for 3 months before prostatectomy. Patients had localized prostate cancer and had chosen radical prostatectomy as primary treatment. The primary end point was treatment effect on intratumoral dihydrotestosterone levels.Results: Intratumoral DHT levels were higher in the degarelix arm than both the degarelix/bicalutamide and LHRH agonist/bicalutamide arms (0.87 ng/g vs. 0.26 ng/g and 0.23 ng/g, P < 0.01). No significant differences existed for other intratumoral androgens, such as testosterone and dehydroepiandrosterone. Patients in the degarelix-only arm had higher AMACR levels on immunohistochemical analysis (P = 0.01). Serum FSH levels were lower after 12 weeks of therapy in both degarelix arms than the LHRH agonist/bicalutamide arm (0.55 and 0.65 vs. 3.65, P < 0.01), and inhibin B levels were lower in the degarelix/bicalutamide arm than the LHRH agonist/bicalutamide arm (82.14 vs. 126.67, P = 0.02).Conclusions: Neoadjuvant degarelix alone, compared with use of LHRH agonist and bicalutamide, is associated with higher levels of intratumoral dihydrotestosterone, despite similar testosterone levels. Further studies that evaluate the mechanisms behind these results are needed. Clin Cancer Res; 23(8); 1974–80. ©2016 AACR.