Impact of Proton Pump Inhibitor Use on the Efficacy of IO–IO Versus IO–TKI Therapy in Metastatic Renal Cell Carcinoma

Basckground Immune checkpoint inhibitor (ICI)-based combination therapies have become the standard first-line treatment for metastatic renal cell carcinoma (mRCC). Proton-pump inhibitors (PPIs), frequently used to treat gastrointestinal conditions, have been implicated in modulating ICI efficacy, potentially through gut microbiome dysbiosis. However, the impact of PPIs on ICI-based therapies for mRCC remains unclear. Methods This multicenter retrospective cohort study analyzed 427 patients with mRCC classified as intermediate or poor risk according to the IMDC criteria treated with first-line IO-IO (ipilimumab plus nivolumab) or IO-TKI (ICI plus tyrosine kinase inhibitor) therapies. Patients were stratified by PPI use during the 30 days before and including the day of ICI initiation. Overall survival (OS), progression-free survival (PFS), and objective response rate (ORR) were compared between PPI users and nonusers. Results PPI use was significantly associated with shorter OS in patients receiving IO-IO therapy (median OS, 23.34 months vs. not reached; P = .002), but not in those receiving IO-TKI therapy ( P = .909). Multivariate analysis confirmed PPIs as an independent prognostic factor for OS in the IO-IO group (HR, 1.647; 95% CI, 1.007-2.693; P = .046). No significant differences in PFS or ORR were observed between PPI users and nonusers in either group, although the complete response rate was notably lower in PPI users treated with IO-IO (1.6% vs. 10.3%; P = .025). Conclusions PPI use was associated with inferior survival in mRCC patients receiving IO-IO therapy, potentially through microbiome modulation and other immunologic or clinical mechanisms; however, these findings are based on retrospective data and should be regarded as hypothesis-generating. Caution is advised when prescribing PPIs to patients undergoing ICI-based therapy, particularly IO-IO regimens, and prospective studies are needed to confirm whether avoiding unnecessary PPI use can improve clinical outcomes.