Background: Dipeptidyl peptidase IV (DPP4) is a cell surface receptor with exopeptidase activity that is expressed on most cell types, and possesses numerous substrates including growth factors, chemokines, and vasoactive peptides. These effects have implicated DPP4 in tumor growth and metastasis. Prior SEER-Medicare and retrospective studies have suggested an association between DPP4 inhibition and increases in both progression-free survival (PFS) and overall survival (OS) in patients with colorectal and lung cancers. Similar studies have shown no associated OS benefit from DPP4 inhibition in breast or pancreatic cancers, and increased OS but not PFS in prostate cancer. However, no studies to date have explored the impact of DPP4 inhibitors (DPP4i) in renal cell carcinoma (RCC). Thus, in this study we present a first-time analysis examining the impact of DPP4i use on PFS in patients with metastatic RCC and type 2 diabetes mellitus. Methods: We performed a single-center retrospective analysis of patients with diabetes and metastatic RCC at University of Virginia. The control group included patients who were on metformin, a sulfonylurea or SGLT2 inhibitor during treatment for metastatic RCC, while the study group included those who were taking a DPP4i with or without metformin and other diabetes medications during treatment. The primary and secondary endpoints of this study were PFS and OS, respectively. Results: Fifty-nine patients were eligible for the study, 11 of whom were taking a DPP4i with or without other diabetic medications during RCC treatment, while 48 were taking metformin with or without other non-DPP4i medications. Cancer progression occurred in 81.8% of patients in the DPP4i group compared to 66.7% of patients in the control group with an odds ratio of 1.58 (95% CI: 0.672-3.71), p = 0.57. No statistically significant difference on PFS (HR: 1.60; 95% CI: 0.75-3.43; p = 0.24) or OS (HR of death: 0.73; 95% CI: 0.27-1.97; p = 0.52) was found in this study. Conclusions: This retrospective study explored the effect of DPP4i on outcomes in patients with metastatic RCC and diabetes. While DPP4i have been shown in previous SEER-Medicare and retrospective studies to have favorable effects on PFS and OS in certain cancers such as colorectal and lung, the results of this study suggest that DPP4i do not confer clinical benefit in patients with RCC, similar to pancreatic and breast cancers. Given the small sample size in this study, larger studies are warranted to better elucidate the effect of DPP4i in metastatic RCC as well as the mechanisms underlying differential tumor response to these agents.