Effective long-term androgen suppression in men with prostate cancer usinga hydrogel implant with the GnRH agonist histrelin

Objectives. To evaluate the effectiveness of a hydrogel implant containing the gonadotropin-releasing hormone (GnRH) agonist histrelin in suppressing testosterone production in men with prostate cancer and to determine the ef fective dose (one, two, or four implants). Methods. Forty-two men with prostate cancer and indications for androgen ab lation were treated with one, two, or four implants. In two of the clinics, comprising 27 subjects, the treatment period was 12 months, with replaceme nt with the same number of implants at 12-month intervals. In a third clini c, which treated 15 subjects, the implants were left in place for up to 30 months. The total experience was 605 treatment months. Results. The histrelin levels were detected in serum proportional to the nu mber of implants placed. The response, however, was similar among all three dose levels, with testosterone and luteinizing hormone essentially complet ely suppressed. Serum testosterone levels decreased from 21.9 +/- 17.6 nmol /L to 0.93 +/- 1.57 nmol/L within I month and were maintained at 0.55 +/- 0 .24 nmol/L at 6 months and 0.60 +/- 0.28 nmol/L after 12 months of treatmen t. Of the 38 assessable patients, 35 (92%) had castrate levels of testoster one within 4 weeks of the initial implant placement. All patients followed for up for 12 months after placement of the initial set of implants maintai ned suppression of testosterone production while the implant was in place. Conclusions. The histrelin hydrogel implant provided adequate and reliable delivery of the potent GnRH agonist histrelin during at least I year using a single implant in men with prostate cancer. No apparent advantages were f ound in using more than one implant, and the question of the possible effec tiveness of even lower doses remains open. This treatment modality appears to be both safe and effective. (C) 2001, Elsevier Science Inc.