Phase Ib (COSMIC-021) trial of cabozantinib (C) in urothelial carcinoma (UC) or C in combination with atezolizumab (A) in patients (pts) with UC, castrate resistant prostate cancer (CRPC) or renal cell carcinoma (RCC).

TPS683Background: 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-naive 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, ...