Long-Term Efficacy and Tolerability of Abdominal Once-Yearly Histrelin Acetate Subcutaneous Implants in Patients with Advanced Prostate Cancer

Objectives. Long-term assessment of the efficacy and tolerability of subcutaneous abdominal histrelin acetate implants that have been inserted for more than two years. Materials and Methods. Retrospective data collected over a six-year period at a single center from charts of 113 patients who received the subcutaneous abdominal histrelin acetate implant. Results. Following insertion of the first implant, 92.1% and 91.8% of patients had a serum testosterone level of ≤30 ng/dL at 24 and 48 weeks, respectively. Serum testosterone levels remained at <30 ng/dL for 96% of patients at two years and for 100% of patients at 3, 4, and 5 years. The testosterone levels remained significantly less than baseline (P < 0.05). Six patients (5.3%) had androgen-independent progression when followed up on the long term, increasing the mean serum PSA at 3, 4, and 5 years to 35.0 µg/L (n = 22), 30.7 µg/L (n = 13), and 132.9 µg/L (n = 8), respectively. The mean serum PSA was significantly greater than baseline during these years (P < 0.05). Eight patients (7.1%) experienced minor, but not serious, adverse events from the histrelin acetate. Conclusion. Subcutaneous abdominal histrelin acetate implants are an effective long-term and well-tolerated administration method for treating patients with advanced prostate cancer.