Background: The role of immune therapy is not established in PRCC. The S1500 (PAPMET) clinical trial established single agent cabozantinib as the standard of care for PRCC (PMID 33592176) with a median progression free survival (PFS) of 9.0 months compared to 5.6 months with sunitinib. Trials have shown activity of PD-(L)1 antagonists as monotherapy (PMID 33529058) or in combination with targeted therapy (PMID 34491815). In a single arm study of cabozantinib/nivolumab the median PFS was 12.5 months (PMID 35298296). There are no prior randomized studies of immune therapy in PRCC. Single arm trials often overestimate the true effect size (PMID 31218346), highlighting the unmet clinical need for a randomized clinical trial in PRCC. We hypothesize that the combination will have higher clinical activity than single agent cabozantinib. Methods: This is a prospective randomized phase II clinical trial conducted through the NCTN and led by SWOG. The primary endpoint is a comparison of PFS between cabozantinib and cabozantinib/atezolizumab. Secondary endpoints include comparison of objective response rate, overall survival and safety. Patients are treated with cabozantinib 60mg/day versus cabozantinib 60mg/day + atezolizumab 1200 mg q3 weeks. 200 patients will be enrolled and randomized 1:1. Key inclusion criteria include a pathologic confirmation of PRCC; presence of metastasis; 0-1 prior systemic lines of therapy for metastatic disease; and measurable disease as defined by RECIST 1.1 criteria. Prior treatment with adjuvant pembrolizumab is allowed if completed greater than 6 months before enrollment. Key exclusion criteria include clinically significant autoimmune disease; ongoing use of strong CYP3A4 inhibitors, strong CYP3A4 inducers. Planned correlatives include stool microbiome testing and genomic/transcriptomic analysis from blood and baseline tissue assays. Clinical trial information: NCT05411081.