Impact of proton pump inhibitors on the onset of gastrointestinal immune‐related adverse events during immunotherapy

Introduction: The gut microbiota (GM) can influence the pathogenesis of immune-mediated adverse events (irAEs). Proton pump inhibitors (PPIs) can affect the integrity of GM, but their role in promoting irAEs is still poorly understood.Methods: In this retrospective single-center cohort study, the primary endpoint was the evaluation of the incidence of gastrointestinal (GI) irAEs in cancer patients on PPIs (exposed) versus cancer patients who were not on PPIs (unexposed).Results: Three hundred and sixty three patients' records (248 M/115F, median age 69) were reviewed. Twenty-three exposed patients (92%) developed GI irAEs while only two unexposed patients (8%) developed GI irAEs (hazard ratio [HR] 13.22, 95% confidence interval [CI] 3.11-56.10, p < 0.000). This HR was confirmed after weighting for the propensity score (HR15.13 95% CI 3.22-71.03, p < 0.000).Conclusion: Chronic PPI use is associated with an increased risk of GI irAES.