Background: The current standard of care in non-progressors to first-line platinum-based chemotherapy for unresectable locally advanced or metastatic urothelial carcinoma (UC) is maintenance treatment with avelumab plus best supportive care (BSC). The Checkmate 032 trial showed that the highest ORR (42.4%) was achieved by the combination of Nivolumab 1 mg/kg and Ipilimumab 3 mg/kg in refractory mUC (1), with a manageable safety profile and better outcomes compared to other treatment arms. The trial aims to consolidate the clinical benefit achieved from first-line chemotherapy with the combination of nivolumab 1mg/kg plus ipilimumab 3mg/kg followed by nivolumab. Methods: This single arm, open-label, multicenter study evaluates the effectiveness of Ipilimumab and nivolumab followed by nivolumab maintenance therapy in delaying disease progression in patients with unresectable urothelial cancer that did not progress after first-line chemotherapy. Main eligibility criteria include: Male or female subjects ≥ 18 yrs old with written informed consent, ECOG performance status 0 or 1, unresectable locally advanced or metastatic transitional cell carcinoma of the urothelium (UCC), patient inclusion within 3-12 weeks after the last chemo dose, no progressive disease per RECIST v1.1, available tumor tissue at baseline, adequate normal organ and marrow function (Haemoglobin ≥ 9.0 g/dL, ANC > 1500 per mm3, platelets ≥ 100,000 per mm3, bilirubin ≤ 1.5 X ULN, transaminases ≤ 2.5X ULN, creatinine clearance > 30 mL/min). The primary endpoint is Progression Free Survival (PFS). Secondary objectives include: objective response rate (ORR), duration of response (DoR), overall survival (OS), chemotherapy overall survival (cOS), and chemotherapy progression-free survival (cPFS). Additionally, the study also has safety secondary objectives. Dynamic biomarker analysis will be performed. As of January 2023, 5 out of the planned 66 patients have been enrolled in the study. 1) Sharma P et al. J Clin Oncol. 2019. Clinical trial information: EudraCT 2021-005364-22.