AbstractObjectiveCheckpoint inhibitors (CPIs) are in widespread clinical use. Little is known about which patients are at risk for developing toxicity. It is essential being able to identify patients with higher risk of experiencing immune‐related adverse events (IRAEs) before initiation of CPI treatment to optimize treatment decisions and follow‐up strategy. The aim of this study was to investigate whether a simplified frailty score based on performance status (PS), age, and comorbidity expressed as Charlson comorbidity index (CCI) could predict development of IRAEs.MethodsWe performed a retrospective cohort study at three Swedish centers. All patients (n= 596) treated with PD‐L1 or PD‐1 inhibitor for advanced cancer between January 2017 and December 2021 were included.ResultsIn total, 361 patients (60.6%) were classified as nonfrail and 235 (39.4%) as frail. The most common cancer type was non‐small cell lung cancer (n= 203; 34.1%) followed by malignant melanoma (n= 195; 32.7%). Any grade of IRAE occurred in 138 (58.7%) frail and in 155 (42.9%) non‐frail patients (OR: 1.58; 95% CI: 1.09–2.28). Age, CCI, and PS did not independently predict the occurrence of IRAEs. Multiple IRAEs occurred in 53 (22.6%) frail and in 45 (12.5%) nonfrail patients (OR: 1.62; 95% CI: 1.00–2.64).DiscussionIn conclusion, the simplified frailty score predicted all grade IRAEs and multiple IRAEs in multivariate analyses whereas age, CCI, or PS did not separately predict development of IRAEs suggesting that this easy‐to‐use score may be of value in clinical decision making but a large prospective study is needed to assess its true value.