Addition of Niraparib to Best Supportive Care as Maintenance Treatment in Patients with Advanced Urothelial Carcinoma Whose Disease Did Not Progress After First-line Platinum-based Chemotherapy: The Meet-URO12 Randomized Phase 2 Trial

Background: Platinum-based chemotherapy (PBCT) is the standard first-line treatment for advanced urothelial carcinoma (UC). Potential cross-sensitivity can be hypothesized between platinum drugs and poly-ADP ribose-polymerase (PARP) inhibitors. Objective: To compare maintenance treatment with the PARP inhibitor niraparib plus best supportive care (BSC) versus BSC alone in patients with advanced UC without disease progression after first-line PBCT. Design, setting, and participants: Meet-URO12 is a randomized, multicenter, open-label phase 2 trial. Patients with advanced UC, without disease progression after four to six cycles of PBCT, with Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1, were enrolled between August 2019 and March 2021. Randomization was stratified by ECOG performance status (0/1) and response to PBCT (objective response/stable disease). Intervention: Patients were randomized (2:1) to experimental arm A (niraparib 300 or 200 mg daily according to body weight and baseline platelets, plus BSC) or control arm B (BSC alone). Outcome measurements and statistical analysis: The primary endpoint was progression-free survival (PFS). The analysis was performed on an intention-to-treat basis. The secondary endpoints reported in this primary analysis are progression-free rate at 6 mo and safety (adverse event rate). Results and limitations: Fifty-eight patients were randomized (39 in arm A and 19 in arm B). The median age was 69 yr, ECOG performance status was 0 in 66% and 1 in 34%; and the best response with chemotherapy was objective response in 55% and stable disease in 45%. The median PFS was 2.1 mo in arm A and 2.4 mo in arm B (hazard ratio 0.92; 95% confidence interval 0.49-1.75, p = 0.81). The 6-mo progression-free rates were 28.2% and 26.3%, respectively. The most common adverse events with niraparib were anemia (50%, grade [G]3 11%), thrombocytopenia (37%, G3-4 16%), neutropenia (21%, G3 5%), fatigue (32%, G3 16%), constipation (32%, G3 3%), mucositis (13%, G3 3%), and nausea (13%, G3 3%). The main limitation of the study is the small sample size: in March 2021, approval of maintenance avelumab for the same setting rendered randomization of patients in the control arm to BSC alone unethical, and accrual was stopped prematurely. Conclusions: Addition of maintenance niraparib to BSC after first-line PBCT did not demonstrate a significant improvement in PFS in patients with UC. These results do not support the conduction of a phase 3 trial with single agent niraparib in this population. Patient summary: In this trial, we tested the efficacy of niraparib as maintenance treatment in patients affected by advanced urothelial cancer after the completion of first-line chemotherapy. We could not demonstrate a significant improvement in progression-free survival with maintenance niraparib.