AbstractBackgroundThe development of immune‐related adverse events (irAEs) may be associated with clinical efficacy of checkpoint inhibitors (CPIs) in patients with cancer. We therefore investigated the effect of irAEs and pre‐treatment parameters on outcome in a large, real‐life patient cohort.MethodsWe performed a single‐centre, retrospective, observational study including patients who received CPIs from 2011 to 2018 and followed until 2021. The primary outcome was overall survival, and the secondary outcome was the development of irAEs.ResultsIn total, 229 patients with different tumour entities (41% non‐small cell lung cancer [NSCLC], 29% melanoma) received a total of 282 CPI treatment courses (ipilimumab, nivolumab, pembrolizumab or atezolizumab). Thirty‐four percent of patients developed irAEs (of these 17% had CTCAE Grade ≥3). Factors independently associated with mortality were pre‐treatment CRP ≥10 mg/L (hazard ratio [HR] 2.064,p= 0.0003), comorbidity measured by Charlson comorbidity index (HR 1.149,p= 0.014) and irAEs (HR 0.644,p= 0.036) (age‐adjusted,n= 216). Baseline eosinophil count ≤0.2 × 109/L was a further independent predictor of mortality (age‐, CRP‐, CCI‐ and irAE‐adjusted HR = 2.252,p= 0.002,n= 166). Anti‐CTLA‐4 use (p< 0.001), and pre‐treatment CRP <10 mg/L were independently associated with irAE occurrence (p= 0.037).ConclusionsWe found an independent association between irAE occurrence and improved overall survival in a real‐life cohort spanning multiple tumour entities and treatment regimens. Pre‐treatment comorbidities, CRP and eosinophil count represent potential markers for predicting treatment response.