Patterns and outcomes of emergency department visits by patients receiving immune checkpoint inhibitors: a single-center, retrospective study.

BACKGROUND: Patients receiving immune checkpoint inhibitor (ICI) therapy may present to the emergency department (ED) for various reasons; however, relevant data from Japan are limited. OBJECTIVES: To investigate ED visits among patients receiving ICI therapy and evaluate the frequency and characteristics of immune-related adverse events (irAEs) diagnosed in the ED. METHODS: We retrospectively reviewed patients who initiated ICI therapy between January and December 2022 and visited the ED through December 2023. Scheduled visits and visits before ICI initiation were excluded. RESULTS: Of 43 patients who visited the ED, 31 (51 ED visits) were analyzed. The median patient age was 74 years, and most patients had an Eastern Cooperative Oncology Group performance status of 0-1. Pain and respiratory symptoms were the most common chief complaints, and 30 visits (58.8%) resulted in hospitalization. The median duration from ICI initiation to the first ED visit was 199 days. Although 14 irAEs occurred in 13 patients, only three ED visits (5.9%; 95% CI, 1.2-16.2%) resulted in a new diagnosis of severe irAEs (grade 3-4): fulminant type 1 diabetes, acute liver failure, and isolated adrenocorticotropic hormone deficiency; these irAEs manifested as nonspecific symptoms. CONCLUSION: irAEs were not the sole reason for ED visits. While the frequency of irAEs diagnosed in the ED was low, all cases were severe, and because the initial symptoms were nonspecific, a careful differential diagnosis was required. ED physicians should systematically confirm current or prior ICI use and perform a broad differential diagnosis to avoid missing severe irAEs.