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

Purpose

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.

Materials and Methods

The 3 cm × 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.

Results

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.

Conclusions

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.

Key Words:  prostate , prostatic neoplasms , drug implants , testosterone , histrelin

Abbreviations and Acronyms:  AJCC, American Joint Committee on Cancer , C_avg, average concentration , GnRH, gonadotropin hormone-releasing hormone , LH, luteinizing hormone , PSA, prostate specific antigen