title: Efficacy of treatment with a GnRH antagonist in prostate cancer patients previously treated with a GnRH agonist.
abstract: OBJECTIVE
  The efficacy of switching from a GnRH agonist to a GnRH antagonist for prostate cancer patients resistant to treatment with the GnRH agonist has not been fully characterized yet. We aimed to evaluate the efficacy of the switch to a GnRH antagonist in patients with PSA failure after hormonal therapy with a GnRH agonist.
  
  
  METHODS
  We retrospectively examined 18 patients with prostate cancer who received androgen-deprivation therapy and who were treated with a GnRH antagonist (degarelix) after they showed an elevated PSA while on GnRH agonist therapy. We evaluated the characteristics of the patients and analyzed some clinical factors for their potential association with the patient response to the switch.
  
  
  RESULTS
  The median PSA at the switch was 7.9 (0.37-1709) ng/ml, and the median testosterone level was 0.17 (<0.08-0.81) ng/ml. Three months after the switch, the median PSA level was 11.3 (0.22-2636) ng/ml, and the median testosterone level was 0.14 (<0.08-0.23) ng/ml. The PSA decreased in six patients (33.3 %) 1 month after the switch, and in three of them it decreased by more than 50 % by 3 months after the switch. Univariate analyses revealed that the lower number of prior treatment lines for prostate cancer before the switch was associated with a favorable decrease in PSA.
  
  
  CONCLUSIONS
  Switching from GnRH agonist to GnRH antagonist therapy was effective for some prostate cancer patients with PSA failure. The small number of prior treatment lines for prostate cancer before the switch was significantly associated with a good PSA response.
authors.affiliation: Department of Urology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors.forename: Taisuke
authors.initials: T
authors.lastname: Ezaki
authors.forename: Takeo
authors.initials: T
authors.lastname: Kosaka
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Mizuno
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Shinojima
authors.forename: Eiji
authors.initials: E
authors.lastname: Kikuchi
authors.forename: Akira
authors.initials: A
authors.lastname: Miyajima
authors.forename: Mototsugu
authors.initials: M
authors.lastname: Oya
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D057915:Drug Substitution; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists / Q000037:antagonists & inhibitors*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009919:Orchiectomy; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000188:drug therapy*; D012189:Retrospective Studies
chemical_list: D007987:Gonadotropin-Releasing Hormone; D017430:Prostate-Specific Antigen