A Case of Switching from GnRH Agonist to Antagonist for Castration Resistant Prostate Cancer Control

GnRH antagonist and GnRH agonist are widely used as androgen deprivation therapy for metastatic prostate cancer. A previous report demonstrated that patients with PSA levels of >20 ng/mL using GnRH antagonists showed favorable outcomes in comparison to those using GnRH agonists. An 82-year old male patient with edema, a stony hard nodule on his prostate, and an initial PSA level of 6,717 ng/mL was referred to our hospital due to suspected prostate cancer. He received prostate needle biopsy and was diagnosed with prostate cancer with bone metastasis, with a Gleason Score of 4 + 4 = 8. He was then treated with a GnRH agonist (leuprorelin acetate) and bicalutamide from July 2015. Although his PSA level decreased to 582.0 ng/mL in December 2015, his PSA level gradually increased and CRPC developed. He indicated that he did not wish to take 2nd generation anti-androgen drugs or receive systemic chemotherapy. We introduced a GnRH antagonist (degarelix) in February 2015; his PSA level did not change and his CRPC was controlled. We herein report a case in which changing a GnRH agonist to a GnRH antagonist contributed to CRPC control.