Background: Combining anti-VEGFR drugs with checkpoint inhibitors have shown synergistic effect in pts with UC. ARCADIA is a phase 2 trial evaluating the safety and efficacy of combination of CABO, a multikinase inhibitor, with the anti-PDL1 DURVA in pts with platinum-refractory advanced UC or variant histology (NCT03824691). Herein we report the preliminary results. Methods: Pts received CABO 40 mg daily, orally, in combination with DURVA 1500 mg, intravenously, every 28 days, until disease progression or unacceptable toxicity. Key inclusion criteria were: ECOG-PS 0-1, UC or variant histology, failure of 1 or 2 platinum-based regimen for metastatic disease, non-measurable disease was permitted. Response was evaluated by RECIST criteria v.1.1 every 2 cycles by CT and ¹⁸FDG PET/CT scans. The primary endpoint of the study was overall survival (OS). Other endpoints included safety, objective response-rate (ORR), duration of response, progression-free survival (PFS). PD-L1 expression was assessed by Ventana SP142 assay. Next-generation sequencing tests (FoundationOne) on pre-therapy tumor samples were performed. Results: From September 2019 to February 2021, 26 pts were enrolled with a median follow-up of 5 mo. Median age was 64 yrs (range 44-74), 69% were male, and 23% had ECOG PS 1. 8 pts presented variant histology. Five pts (19%) had received 2 prior systemic anticancer therapies. In pts evaluable for efficacy analyses, 3 (11.5%) complete responses (CR) and 6 (23.1%) partial responses (PR) were observed. The ORR and DCR were 34.6% and 57.7% respectively. Treatment-related AEs (TRAEs) occurred in 17 pts (65%), including 2 (8%) grade 3 TRAEs, within the first 2 cycles. 7 pts (27%) discontinued CABO due to toxicity, no interruption of DURVA was observed. The most common AEs by any grade were transaminase increase (35.7%), asthenia (27%), diarrhea (27%), and hypertension (15%). Conclusions: Combination of CABO and DURVA demonstrated promising preliminary activity and a manageable safety profile in pts with advanced UC and variant histology. More mature results according to biomarkers and histology will be presented. Clinical trial information: NCT03824691