Efficacy and Safety of Histrelin Subdermal Implant in Patients With Advanced Prostate Cancer

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Abstract
This open label, multicenter study was done to evaluate the efficacy and safety of the gonadotropin hormone-releasing hormone agonist histrelin acetate administered as a 50 mg subdermal implant in men with advanced prostatic cancer. The 3 cm x 3.5 mm histrelin implant was surgically inserted in the inner aspect of the upper nondominant arm of eligible patients under local anesthesia. Patients were evaluated weekly for the first 2 weeks after implant insertion and monthly thereafter. At week 52 the implant was removed and in most cases a new implant was inserted. Patient observation for safety and efficacy continued to week 60. Efficacy was determined by the proportion of patients who attained chemical castration (serum testosterone 50 ng/dl or less) at weeks 4 through 52. Of the 134 patients with week 4 testosterone levels available 100% achieved chemical castration. Testosterone suppression was maintained throughout the 52 weeks after implantation in more than 99% of patients. Significant LH and PSA suppression was also observed. By week 16 PSA had decreased an average of 90% from a baseline of 83.6 ng/ml (p = 0.0001). By week 60, 79% of patients had a complete PSA response (p <0.0175). No testosterone or LH surge was observed with reimplantation. Additionally, the implant was safe and well tolerated. The gonadotropin hormone-releasing hormone agonist histrelin acetate provided in a unique implant delivery device is effective for treating men with advanced prostate cancer, as demonstrated by the suppression of testosterone and LH to castrate levels at 4 weeks and the maintenance of these levels during 52 weeks. PSA, a secondary end point for effectiveness, was also suppressed significantly from baseline.