Background: C is an inhibitor of tyrosine kinases involved in tumor growth, angiogenesis, and immune regulation, including MET, VEGFR, and TAM kinases (Tyro3, AXL, MER). Preclinical and clinical studies suggest that C promotes an immune-permissive tumor environment which may enhance response to immune checkpoint inhibitors (ICI) such as the anti-PD-L1 mAb, A. C is approved for pts with advanced RCC and has shown encouraging clinical activity in combination with a PD-1 targeting mAb in RCC, UC, and CRPC (Nadal et al 2017). A is approved for pts with advanced UC after prior platinum-containing chemo and for chemo-naïve pts with platinum ineligible UC or PD-L1+ cisplatin ineligible UC. Combination of C with A may enhance treatment efficacy in pts with genitourinary (GU) cancers. Here, we present the study design of an ongoing phase 1b trial of C + A which includes cohorts with advanced RCC, UC, and CRPC. Methods: This global multicenter, phase 1b, open-label trial will assess the safety, tolerability, activity, and pharmacokinetics of C or C + A (NCT03170960). The study comprises a dose-escalation stage and an expansion stage. The dose-escalation stage (3+3 design) is completed. C 40 mg qd + 1200 mg A q3w is the recommended dose for the expansion stage. In the expansion stage, 18 cohorts (each 30 pts) will be enrolled including 7 cohorts with GU cancers: (1) treatment naïve clear cell RCC; (2) non-clear cell RCC, treatment naïve or following systemic anticancer therapy; (3) UC after prior platinum-based therapy; (4) treatment naïve cisplatin-ineligible UC; (5) treatment naïve cisplatin-eligible UC; (6) UC after prior ICI therapy and (7) CRPC after prior enzalutamide and/or abiraterone. In addition, an exploratory cohort (30 pts) will evaluate single agent 60 mg C in pts with UC after prior ICI therapy. Pts will continue treatment as long as they experience clinical benefit per investigator or until unacceptable toxicity. The primary objective of the expansion stage is the objective response rate per RECIST 1.1 per investigator for each cohort. Secondary objectives will assess safety including immune related AEs. Clinical trial information: NCT03170960