# Risk factors for immune checkpoint inhibitor colitis: a retrospective multi-center cohort study using electronic health records

## TL;DR

This study identifies risk factors for colitis caused by immune checkpoint inhibitors, including antibiotic use and GI disorders, to help improve patient care.

## Contribution

A multi-center cohort study using electronic health records to identify novel risk factors for ICI-induced colitis.

## Key findings

- Concurrent antibiotic use and NSAIDs significantly increase the risk of ICI colitis.
- Gastrointestinal disorders like GERD and gallbladder disease are notable risk factors.
- BMI changes before and after ICI administration correlate with CIC risk.

## Abstract

Immune checkpoint inhibitors (ICIs) are effective for many cancers but often cause immune-related adverse events, particularly gastrointestinal (GI) complications such as colitis. Identifying risk factors for ICI colitis (CIC) could improve patient selection and discover potential mechanisms relevant to idiopathic inflammatory bowel disease (IBD). We aim to identify risk factors with a robust methodological approach in a large multi-center longitudinal cohort.

We used electronic health record data from six University of California institutions with 10,260 adults on ICIs. Baseline and time-varying predictors were defined based on prior IBD epidemiology studies, including interactions. LASSO Cox regression was applied to data from UCSF Central Data Warehouse to select the most predictive model, with coefficients estimated using multi-center data.

Fourteen significant predictors of CIC were identified. The strongest predictors were concurrent use of antibiotics (HR 2.72, 95% CI: 2.41–3.07) and non-steroid anti-inflammatory drugs (1.50, 1.16–1.94). Notable GI risk factors included gastroesophageal reflux disorder (1.31, 1.14–1.50), other GI disorders (1.32, 1.16–1.50), and disorders of the gallbladder, biliary tract, and pancreas (1.33, 1.15–1.57). High BMI before ICI administration increased risk (per unit 1.07, 1.04–1.09), while higher BMI after ICI administration decreased risk (per unit 0.93, 0.90–0.95). Melanoma, anxiety, and depression also increased risk. GI oncologists should consider ICI colitis in patients with comorbid GI disorders or those using antibiotics or NSAIDs. A routine checkup for colitis could be beneficial for those patients. Future studies are needed to explore the underlying mechanisms and quantify clinical impact of increased checkups for colitis.

The online version contains supplementary material available at 10.1007/s00262-026-04359-2.