Incidence of immune-related adverse events in U.S. veterans treated with immune checkpoint inhibitors

Immune checkpoint inhibitors (ICIs) are associated with potentially severe immune-related adverse events (irAEs). Emerging clinical practice reports have suggested higher incidence of irAEs in real-world settings than initially observed in phase III clinical trials. Objectives were to determine the incidence of irAEs associated with ICIs in a clinical population, the Veterans Health Administration, characterize their time to onset, and explore potential risk factors.

This retrospective observational study included patients from eight Midwest VA medical centers who initiated an ICI between January 1, 2014, and June 30, 2022. Courses of incident prednisone therapy lasting at least seven days at a dose ≥ 20 mg/day were used to identify irAEs, within two years following ICI initiation. A multivariate Cox proportional hazards regression model was used to explore potential irAE risk factors.

Of 1314 patients, the incidence of irAEs was 19.8%, with most (86.5%) occurring within one year of ICI initiation. Monthly incidence rates peaked three months following ICI initiation at 3.0% and decreased thereafter. Female gender (hazard ratio [HR] = 2.01, 95% confidence interval [CI]: 1.01-4.00) and combination therapy with ipilimumab and nivolumab (HR = 2.46, 95% CI: 1.44-4.21) were significantly associated with irAE incidence.

These findings are consistent with recent studies in clinical populations that demonstrate higher irAE incidence rates than originally reported in clinical trials. Our findings may enhance prompt recognition and treatment of irAEs for VA patients.