Clinical study of leuprolide depot formulation in the treatment of advanced prostate cancer. The Leuprolide Study Group.

In a phase III, open, multicenter study we evaluated the safety and efficacy of the depot formulation of leuprolide (7.5 mg. injected intramuscularly every 4 weeks) in patients with stage D2 prostate cancer who had not previously received systemic treatment. Serum testosterone, luteinizing hormone and plasma leuprolide levels were monitored during the 24-week study period. Median interval to onset of castrate testosterone levels was 21 days and mean testosterone levels decreased to within the castrate range by week 3 of treatment. After onset of castrate levels there were no escapes (defined as 2 consecutive values of greater than 50 ng./dl.) of testosterone levels during the 24 weeks. Suppression of testosterone did not differ significantly from that observed in patients receiving the daily subcutaneous injection of leuprolide acetate in the first 24 weeks of another study. Objective response (no progression) to treatment occurred in 81% of 53 evaluable patients and adverse (related and unrelated) events were reported in 45 of the 56 patients. The response rate and incidence of adverse events in this study did not differ significantly from those occurring with the daily formulation. We conclude that the depot formulation of leuprolide is safe and effective in the treatment of advanced prostatic cancer, and that the safety and efficacy of this formulation do not differ significantly from those of the daily subcutaneous formulation.