Objective. To evaluate the safety and efficacy of the highly selective oral gonadotropin-releasing hormone (GnRH) antagonist relugolix in men with advanced prostate cancer.
Design. Global, multicenter, randomized, open-label, phase 3 trial.
Intervention. Patients were randomized in a 2:1 ratio to receive either relugolix 120 mg once daily after receiving a single loading dose of 360 mg, or 22.5 mg of leuprolide acetate every 3 months. Patients in Japan and Taiwan received 11.25 mg of leuprolide. The randomization was stratified by age (> 75 years or ≤ 75 years), metastatic disease status, and geographic region (Asia, Europe, North and South America). The intervention period was 48 weeks.
Setting and participants. 1327 patients were screened, and 934 patients underwent randomization: 622 patients to the relugolix group and 308 to the leuprolide group. Patients had histologically or cytologically confirmed adenocarcinoma of the prostate. All patients had to have 1 of the following: evidence of biochemical or clinical relapse after primary curative therapy, newly diagnosed hormone-sensitive metastatic disease, or advance localized disease unlikely to be cured by local primary intervention. The patients with disease progression or rising prostate-specific antigen (PSA) had the option to receive enzalutamide or docetaxel after the confirmation of progression. Patients were excluded if they had a major cardiovascular event within 6 months of enrollment.
Main outcome measures. The primary endpoint was sustained castration rate, defined as the cumulative probability of testosterone suppression to ≤ 50 ng/dL while on study treatment from week 5 through week 48. Secondary endpoints included noninferiority of relugolix to leuprolide in regard to sustained castration rate. Superiority testing was performed if the noninferiority margin of –10 percentage points was met. Additional secondary endpoints were probability of testosterone suppression to ≤ 50 ng/dL on day 4 and day 15 and the percentage of patients with a > 50% decrease in PSA at day 15 and follicle-stimulating hormone (FSH) levels at the end of week 24.
Main results. The baseline characteristics were well balanced between the treatment groups. Approximately 30% of the patients in each group had metastatic disease. Approximately 50% of patients enrolled had biochemical recurrence following primary treatment for prostate cancer. The mean PSA was 104.2 ng/mL in the relugolix group and 68.6 ng/mL in the leuprolide group. The majority of patients had at least 1 cardiovascular risk factor (ie, tobacco use, obesity, diabetes, hypertension, or a history of a major adverse cardiac event [MACE]). Adherence to oral therapy was reported as 99% in both groups. The median follow-up time was 52 weeks; 90% of patients in the relugolix arm and 89% in the leuprolide arm completed 48 weeks of treatment.
Sustained testosterone suppression to ≤ 50 ng/dL from day 29 through week 48 was seen in 96.7% of patients in the relugolix group and 88.8% in the leuprolide group, which was determined to be noninferior. Additionally, relugolix was also found to be superior to leuprolide in regard to sustained testosterone suppression (P < 0.001). These results were consistent across all subgroups. Relugolix was also found to be superior to leuprolide for all secondary endpoints, including cumulative probability of castration on day 4 (56% vs 0%) and day 15 (98.7% vs 12%) and testosterone suppression to ≤ 20 ng/dL on day 15 (78.4% vs 1%). Confirmed PSA response on day 15 was seen in 79.4% of patients in the relugolix arm and in 19.8% in the leuprolide arm (P < 0.001). FSH suppression was greater in the relugolix arm compared with the leuprolide arm by the end of week 24. An increase of testosterone levels from baseline was noted in the leuprolide patients at day 4, with the level decreasing to castrate level by day 29. In contrast, relugolix patients maintained castrate testosterone levels from day 4 throughout the intervention period. Testosterone recovery at 90 days was seen in 54% of patients in the relugolix group compared with 3% in the leuprolide group (P = 0.002).