Occurrence of Possible Rheumatologic Immune-Related Adverse Events (rh-irAEs) Associated with Immune Checkpoint Inhibitor (ICI) Therapy

INTRODUCTION: Current epidemiologic literature of rheumatologic immune-related adverse events (rh-irAEs) consists of clinical trials, case reports, or smaller, single-center series. We evaluate the occurrence of rh-irAEs during immune checkpoint inhibitor (ICI) therapy from US commercial claims data. METHODS: Patients newly initiating ICI therapy in commercial claims data were eligible for inclusion. Rh-irAEs were defined using ≥ 1 International Classification of Diseases (ICD)-9 or ICD-10-Clinical Modification (CM) claims for selected events, ranging from joint pain and myalgia to ankylosing spondylitis and psoriasis. The percentage of patients experiencing rh-irAEs after ICI initiation was determined. RESULTS: A total of 5722 patients initiating an ICI between January 1, 2012, and June 30, 2018, were included; 201 patients (3.5%) had a history of rheumatic disease. Among the 5521 patients without a history of rheumatic disease, 29.6% experienced ≥ 1 rh-irAE in follow-up, decreasing to 22.6% when assessing events for which there was no diagnostic history. Limiting to claims for rh-irAE with a rheumatologist provider, the proportion of patients experiencing an event decreased to 0.9%. Among patients with a history of rheumatic disease, 71.6% experienced ≥ 1 rh-irAE. Limiting to events for which the patient did not have a history during baseline, 35.3% experienced an event. CONCLUSIONS: Occurrence of rh-irAEs during ICI use is higher in patients with pre-existing rheumatic disease compared to those with no pre-existing rheumatic disease. However, the most common events were not definitive rheumatic diseases but rather symptoms, such as pain in joints. Occurrence of events associated with a rheumatologist provider was substantially lower, suggesting that either patients are not referred to a rheumatologist or referral does not result in confirmation of the diagnosis by the rheumatologist. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40744-021-00359-z.