Multicenter phase II study of trabectedin in patients with metastatic castration-resistant prostate cancer

Background: This multicenter phase II trial evaluated the efficacy and safety of trabectedin in metastatic castration-resistant prostate cancer (CRPC). Patients and methods: Two schedules were evaluated in three cohorts: weekly as 3-h i.v. infusion at 0.58 mg/m ² for 3 out of 4 weeks (Cohort A, n = 33), and every 3 weeks (q3wk) as 24-h infusion at 1.5 mg/m ² (Cohort B1, n = 5) and 1.2 mg/m ² (Cohort B2, n = 20). The primary end point was prostate-specific antigen (PSA) response; secondary end points included safety, tolerability and time to progression (TTP). Results: Trabectedin resulted in PSA declines ≥50% in 12.5% (Cohort A) and 10.5% (Cohort B2) of patients. Among men pretreated with taxane-based chemotherapy, PSA response was 13.6% (Cohort A) and 15.4% (Cohort B2). PSA responses lasted 4.1-8.6 months, and median TTP was 1.5 months (Cohort A) and 1.9 months (Cohort B2). The dose of 1.5 mg/m. ² (approved for soft tissue sarcoma) given as 24-h infusion q3wk was not tolerable in these patients. At 1.2 mg/m. ² q3wk and 0.58 mg/m. ² weekly, the most common adverse events were nausea, fatigue and transient neutropenia and transaminase increase. Conclusions: Two different trabectedin schedules showed modest activity in metastatic CRPC. Further studies may require identification of predictive factors of response in prostate cancer.