Risk factors of immune-related adverse events in patients with early-stage breast cancer: Findings from a multi-institutional retrospective study

INTRODUCTION: Identifying risk factors and biomarkers of immune-related adverse events (irAE) in patients with early-stage breast cancer could help prevent and mitigate irAE and improve disease outcomes. This retrospective cohort study aims to identify predictive biomarkers of irAE in patients with early-stage breast cancer treated with ICI. METHODS: Patients with early-stage breast cancer treated with ICI between 2014 and 2024 from four institutions were included. Demographics, baseline laboratory values, and ICI treatment information were collected. Chi-square and Wilcoxon rank-sum tests were used to compare patients with and without any-grade irAE and grade ≥3 irAE. Uni- and multivariate logistic regression was performed to determine factors predictive of grade ≥3 irAE. RESULTS: Of the 423 patients included, 307 (72.6%) developed any-grade irAE and 81 (19.1%) developed grade ≥3 irAE. Hispanic ethnicity was associated with lower rates of any-grade and grade ≥3 irAE compared to non-Hispanic/unknown ethnicity (p < 0.0001 and p = 0.04, respectively). Patients with higher absolute eosinophil counts were more likely to have any-grade irAE (p = 0.0005). Grade ≥3 irAE were more common in non-smokers (p = 0.05) and those with chronic kidney disease (CKD; p = 0.001). Multivariate logistic regression demonstrated that older age (≥50y vs. <50y) [OR 1.70; 95% CI, 1.02-2.85; p = 0.04] and CKD (OR 4.97; 95% CI, 1.59-15.5; p = 0.006) were predictive of grade ≥3 irAE. CONCLUSION: In patients with early-stage breast cancer treated with ICI, older age and the presence of CKD were risk factors of grade ≥3 irAE. Further studies to identify biomarkers of irAE are needed to prevent irAE and reduce the long-term complications.