The association between metformin use, immune mediated colitis and overall survival in patients treated with checkpoint inhibitor

Introduction: Metformin is frequently prescribed to treat type 2 diabetes. Its primarily regulates hepatic and colonic glucose metabolism, but recent studies have suggested an anti-inflammatory effect, especially in colitis. It has been suggested that metformin may enhance immune checkpoint inhibition (ICI) efficacy for cancer treatment. Our study aims to explore the impact of metformin on ICI efficacy and the risk for colitis. Methods: This was a single center, retrospective analysis of consecutive patients at a tertiary cancer center who received ICI between 01/2010–12/2022 and developed immune-mediated colitis (IMC). Patients were screened for colitis based on stool tests, then divided into two groups depending on metformin use prior to colitis onset. We collected data on demographic and colitis clinical information including treatments, and outcomes. Results: A total of 953 patients were included. The incidence of IMC was higher among metformin users (7.6 %) than non-metformin users (4.9 %; p < 0.01). There were no significant differences in colitis features and outcomes, except for longer hospital stay among metformin users (8 days vs 6 for non-metformin users; p = 0.03). Metformin use was associated with shorter overall survival vs non-metformin users among patients with IMC (p = 0.03). Discussion: Our study is among the first to explore the impact of metformin on IMC and overall survival. We found that metformin use may be associated with higher risk of IMC. We also found an association between metformin use and shorter overall survival among patients who developed IMC. Larger studies with risk-stratified analysis are needed to validate our findings.