Testosterone castration levels in patients with prostate cancer: Is there a difference between GnRH agonist and GnRH antagonist? Primary results of an open-label randomized control study.

Purpose: To compare testosterone castration levels between patients treated with the gonadotropin-releasing hormone (GnRH) antagonist, degarelix, and GnRH agonist.

Materials and methods: Patients with prostate cancer (PCa) of a single outpatient clinic were randomized (2:1) to receive degarelix (group A) or GnRH agonist (group B). The study evaluated testosterone and prostate-specific antigen (PSA) levels, patients' age, Gleason score and the presence of metastases (nodal or bone). Testosterone and PSA levels were measured at 1st, 6th, 12th, and 18th months. Mann-Whitney test and Spearman correlation were used to investigate independent variable while standard multiple regression was performed to explore statistically significant correlations. Kruskal-Wallis test was used to compare testosterone levels at follow-up.

Results: The study included 168 patients, 107 in group A and 61 in group B. Testosterone levels at 1st month were significantly lower in patients under GnRH antagonist than those receiving GnRH agonist (group A: 22 ng/dL vs. group B: 29 ng/dL, p=0.011). However, PSA values did not differ significantly between groups (group A: 0.130 ng/mL vs. group B: 0.067 ng/mL, p=0.261). In multivariate analysis, treatment with degarelix was an independent factor of lower testosterone levels at 1st month (p=0.013). Comparison of testosterone levels at 6, 12, and 18 months did not reveal any significant difference within each group.

Conclusions: In patients with PCa who are candidates for androgen deprivation therapy, the administration of GnRH antagonist seems to achieve significantly lower testosterone levels compared to treatment with GnRH agonist at 1st month of treatment.