A switch from GnRH agonist to GnRH antagonist in castration-resistant prostate cancer patients leads to a low response rate on PSA

Abstract

Switch from an agonist to an antagonist of GnRH has a limited impact on PSA at 3 months in castration-resistant prostate cancer patients.

Efficacy of treatment with a GnRH antagonist in prostate cancer patients previously treated with a GnRH agonist

“…The rate of patients who reached this 50 % value in our study was better compared with that in a previous study, in which only 5.8 % (one out of 17 patients) reached a 50 % PSA decrease [3]. This might be because of differences in the inclusion criteria.…”

“…But another paper described that the switch from GnRH agonist to GnRH antagonist had a limited effect on the PSA level in CRPC patients [3]. We considered that it was essential to identify the efficacy of the switch and retrospectively examine its efficacy in prostate cancer patients with PSA failure after ADT.…”

“…Since the emergence of GnRH antagonists, switching from a GnRH agonist to a GnRH antagonist has been tried for patients resistant to GnRH agonists [3]. There have been some case reports of patients with metastatic prostate cancer who failed to achieve castrate levels of testosterone on a GnRH agonist but subsequently responded to a GnRH antagonist [4].…”

An Unusual Prostate-Specific Antigen Decrease in an Advanced Castration-Resistant Prostate Cancer Patient with Intracerebral Hemorrhage Subsequently Treated with Luteinizing Hormone-Releasing Hormone Antagonist

“…The LH-RH antagonist may have contributed to the 56% decrease in PSA, from 1,235 to 540 ng/ml. Two previous studies indicated that switching from LH-RH agonist to LH-RH antagonist could decrease PSA levels in CRPC patients [5, 6]. Degarelix, which is a recently developed LH-RH antagonist, showed a significantly lower risk of PSA progression or death in a certain population when compared with the LH-RH agonist [7].…”

“…The difference in effect between LH-RH agonist and antagonist could be explained by (1) a loss of testosterone surge or a reduction of testosterone, (2) the suppression of follicle-stimulating hormone and (3) a direct effect of the LH-RH antagonist on the LH-RH receptors in the prostate cancer cells [2]. A previous study indicated the possibility of a slight change in testosterone level being a cause of PSA decrease [5]. However, PSA levels in these previous studies were 3–60 ng/ml upon commencement of LH-RH antagonist administration [5, 6].…”