SOGUG-Vexillum: Phase II non-randomized clinical trial of nivolumab/ipilimumab maintenance following first-line chemotherapy in unresectable locally advanced or metastatic urothelial cancer.

4576 Background: Nivolumab (nivo) 1mg/kg plus ipilimumab (ipi) 3mg/kg achieved the highest ORR (42.4%) in refractory metastatic urothelial carcinoma (mUC) with a manageable safety profile. The addition of nivo and ipi subsequently to first-line chemotherapy (CT) could consolidate the clinical benefit. Methods: This single arm, open-label, multicenter study evaluates the effectiveness of ipi 3 mg/kg and nivo 1 mg/kg (Q3W) for 4 cycles followed by nivo maintenance therapy (Q4W) in delaying disease progression in patients with unresectable urothelial cancer that did not progress after first-line platinum-based CT (at least 4-6 cycles of CT). Autoimmune disease, immune deficiency, and symptomatic brain metastasis were excluded. The primary endpoint is Progression Free Survival (PFS) in intention-to-treat and PD-L1 populations. Secondary endpoints include: objective response rate (ORR), duration of response (DoR), overall survival (OS), overall survival from 1 st dose of CT (cOS), progression-free survival from 1 st dose of CT (cPFS), safety and translational biomarker analysis. Sample size was estimated using a Simon II stage design for 4-months PFS rate (H0= 40%; H1= 60; α= 0.05; β= 80%; attrition 10%), requiring 25 patients in the 1 st stage and up to 66 in total. Here we report the interim analysis for 1 st stage. Results: As of January 2024, the 1 st accrual stage was completed with 25 evaluable patients. Baseline characteristics are outlined in the table. With a median follow-up of 6.8 months (95% CI: 6.2-10.5), the 4-m PFS rate was 64% (95% CI: 47.7-85.9) and the median PFS was 4.3 months (95% CI: 3.2-NR). The median cPFS was 9.4 months (95% CI: 8-NR). The 6-m OS rate was 76.4% (95% CI: 60-97.2), while median cOS was 15.4 months (95% CI: 15.4-NR). The median duration of treatment was 2.6 months (95% CI: 2.1, 5.7). Nivo and ipi were permanently discontinued due to toxicity in 3 (12%) and 1 (4.2%) patients, respectively. Nivo doses were delayed in 8 (32%) patients and ipi in 3 (12%) for management of toxicity. Grade ≥3 toxicities were reported in 8 (32%) patients, being the most common: Immune-mediated hepatitis (8%), ALT/AST increased (8%) and diarrhea (8%). Conclusions: Maintenance treatment with nivo and ipi showed preliminary efficacy consolidating clinical benefit to CT with a manageable safety profile. The 4-m PFS rate surpassed the futility threshold in the interim analysis and the accrual in Stage II is underway. Final survival results are awaited. Clinical trial information: NCT05219435 . Table: see text