Efficacy and safety of leuprorelin acetate 6-month depot in prostate cancer patients: a Phase III, randomized, open-label, parallel-group, comparative study in Japan

OBJECTIVE Leuprorelin acetate (TAP-144-SR) is commonly used worldwide in prostate cancer patients. This study was conducted to assess the non-inferiority of a 6-month depot formulation of TAP-144-SR (TAP-144-SR [6M]) 22.5 mg to a 3-month depot formulation of TAP-144-SR (TAP-144-SR [3M]) 11.25 mg in prostate cancer patients in Japan. METHODS This was a 48-week Phase III, open-label, parallel-group comparative study. TAP-144-SR (6M) 22.5 mg (6M group) and TAP-144-SR (3M) 11.25 mg (3M group) were administered to 81 and 79 subjects, respectively. The primary endpoint was the rate of serum testosterone suppression to the castrate level (≤100 ng/dl). RESULTS Serum testosterone of all subjects excluding one subject in the 3M group was suppressed to the castrate level throughout 48 weeks. The estimated between-group difference (6M group - 3M group) in suppression rate was 1.3% (95% confidence interval: -3.4, 6.8), and its lower confidence interval was more than -10% of the pre-determined allowable limit value to judge the non-inferiority. The prostate-specific antigen concentrations were stable throughout the study in both groups. Progressive disease in the best overall response based on the Response Evaluation Criteria In Solid Tumors was 0.0% for the 6M group and 2.6% for the 3M group. Adverse events occurred in 92.6% in the 6M group and 89.9% in the 3M group. Adverse events leading to discontinuation were reported in 2.5% in the 6M group and 3.8% in the 3M group. CONCLUSIONS TAP-144-SR (6M) was not inferior to TAP-144-SR (3M) for the suppressive effect on serum testosterone level. TAP-144-SR (6M) was also as well tolerated as TAP-144-SR (3M).