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

Purpose

At the time of castration resistance, it is recommended to realize hormonal manipulations before chemotherapy. We evaluated the impact of a switch from GnRH agonist to antagonist in patients with castration-resistant prostate cancer on PSA and testosterone levels at 3 months.

Methods

Retrospectively, 17 patients from 5 different centers undergoing androgen deprivation therapy and presenting rising PSA confirmed on 3 blood samples 2 weeks apart and despite a castrate testosterone level (<0.5 ng/ml) were reviewed. Antiandrogen withdrawal syndrome had been tested before the switch. Degarelix was administered as followed: 240 mg for the first injection and then 80 mg every month, subcutaneously. We evaluated the PSA and testosterone level variation 3 months after the switch. Patients who experienced a variation in PSA of less than 10% compared to the baseline or who had a more than 10% PSA decrease were defined as responders.

Results

Mean PSA level at the switch was 34.3 ± 50.3 ng/ml, with a mean testosterone level of 0.21 ± 0.13 ng/ml. Three months after the switch, mean PSA level was 59.9 ± 81.6 ng/ml (P = 0.061), with a mean testosterone level of 0.19 ± 0.08 ng/ml (P = 0.086). At 3 months, 4 patients (23%) responded to therapy. Thirteen patients (77%) experienced a rise in PSA of more than 10% compared to baseline; 41% of patients decreased their testosterone level. The limitations of this study are its retrospective nature and the limited number of patients.

Conclusion

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