Worse Survival and Gastrointestinal Toxicity Outcomes Among Patients Receiving Proton Pump Inhibitors During Checkpoint Inhibitor Therapy.

Background: Immune checkpoint inhibitors (ICIs) for cancer carry a risk of immune-related adverse events (irAEs). Upper and lower gastrointestinal tract inflammation are common toxicities. Proton pump inhibitors (PPIs) are used to treat upper gastrointestinal irAEs. Studies have suggested these agents may also worsen lower gastrointestinal irAEs. Our study evaluated the effect of PPI exposure on gastrointestinal irAE severity.

Methods: This was a single-center retrospective chart review including all patients receiving ICIs between January 2010 and February 2024 who developed upper or lower gastrointestinal toxicity. Patients were grouped based on PPI use, defined as receiving a PPI any time from 3 months before ICI initiation until gastrointestinal toxicity diagnosis.

Results: A total of 1,228 patients were included: 88 (7.2%) with upper gastrointestinal toxicity and 1,140 (92.8%) with lower toxicity. Upper gastrointestinal irAEs were more severe among PPI users (69.6% with grade 3 toxicity in the PPI group vs 29.6% in the non-PPI group; P<.05). Similarly, lower gastrointestinal irAEs were more severe among PPI users, with a higher need for multiple lines of biologic treatment, higher hospitalization rates, and longer hospital stays (P<.05 for all). PPI use was associated with significantly worse overall survival among patients receiving ICIs (P<.05).

Conclusions: Our study is the largest to date showing the impact of PPI use on immunotherapy toxicity. PPI use may predispose to more severe toxicities and worse outcomes. PPIs may also reduce immunotherapy efficacy, as reflected by worse overall survival. These findings support the judicious use of PPIs in patients receiving ICIs and call for prospective studies to validate our results.