Purpose: We determined the duration of testosterone suppression and recovery in patients with prostate cancer treated with a hydrogel implant releasing the gonadotropin releasing hormone (GnRH) agonist histrelin or treated with a depot GnRH agonist.
Materials and methods: Luteinizing hormone (LH) and testosterone (T) responses were monitored in 3 groups. Group 1 comprised 7 patients treated with histrelin implant, which is inserted into the arm of the patient while under local anesthesia, and suppresses LH and testosterone. Following implant removal antiandrogens (flutamide or bicalutamide) were administered. Group 2 comprised 8 patients treated with long-term depot GnRH super agonists which were later withheld and patients were given bicalutamide. Group 3 consisted of 7 patients treated with bicalutamide.
Results: In group 1 LH and T were in the castration range while implants were in place. LH increased 1 to 6 weeks after implant removal followed by an increase in T. In 7 of 8 patients in group 2, LH, T and prostate specific antigen remained suppressed for 9 months. In 6 of 7 group 3 patients LH and T increased with a decrease in prostate specific antigen.
Conclusions: Despite continuous prolonged T suppression for up to 3 years due to histrelin implant, LH and T increased rapidly following implant removal, indicating that suppression is reversible. In view of the 9-month suppression of LH and T after the last depot GnRH injection in 7 of 8 patients, it is possible to space GnRH agonist administration at longer intervals. However, T must be monitored to determine that suppression is maintained.