Objectives We sought to estimate the prevalence of patients with cancer presenting to the emergency department (ED) who are undergoing treatment with immune checkpoint blockade (ICB) therapy; report their chief complaints; describe and estimate the prevalence of immune-related adverse events (IRAEs).

Methods Four abstractors reviewed the medical records of patients with cancer treated with ICB who presented to an ED in Paris, France between January 2012 and June 2017. Chief complaints, underlying malignancy and ICB characteristics, and the final diagnoses according to the emergency physician were recorded. Abstractors noted if an emergency physician identified that a patient was receiving an ICB and if the emergency physician considered the possibility of an IRAE. The gold standard as to whether an IRAE was the cause was the patients’ referring oncologist’s opinion that the ED symptoms were attributed to ICB and IRAE according to post-ED medical records. Descriptive statistics were reported.

Results Among the 409 patients treated with ICB at our institution, 139 presented to the ED. Chief complaints were fatigue (25.2%), fever (23%), vomiting (13.7%), diarrhoea (13.7%), dyspnoea (12.2%), abdominal pain (11.5%), confusion (8.6%) and headache (7.9%). Symptoms were due to IRAEs in 20 (14.4%) cases. The most frequent IRAEs were colitis (40%), endocrine toxicity (30%), hepatitis (25%) and pulmonary toxicity (5%). Patients with IRAEs compared with those without them more frequently had melanoma; had received more distinct courses of ICB treatment, an increased number of ICB medications and ICB cycles; and had a shorter time course since the last infusion of ICB. Emergency physicians considered the possibility of an IRAE in 24 (17.3%) of cases and diagnosed IRAE in 10 (50%) of those with later confirmed IRAE. IRAE was more likely to be missed when the referring oncologist was not contacted or when the patient had respiratory symptoms, fatigue or fever.

Conclusions ICB exposes patients to potentially severe IRAEs. Emergency physicians must identify patients treated with ICB and consider their toxicity when patients present to the ED with symptoms compatible with IRAEs.