P025 Immune-related adverse events: experiences within a tertiary centre rheumatology clinic

Abstract Background/Aims Immune checkpoint inhibitors (ICIs) have transformed cancer therapy but are frequently associated with immune-related adverse events (irAEs) resembling primary rheumatological diseases. Rheumatology services play a central role in managing these complications associated with significant burden of morbidity and potential to disrupt oncological treatment. Despite increasing clinical exposure, data on the real-world presentation and management of rheumatological irAEs remain limited. The aim of this audit was to characterise the clinical features, timing, and treatment requirements of patients referred with suspected rheumatological irAEs in a tertiary centre rheumatology clinic. Methods We conducted a retrospective review of 27 consecutive patients - without prior autoimmune rheumatological disease - referred to the rapid-access rheumatology hot clinic between February 2023 and August 2025. Demographic data, underlying malignancy, ICI therapy, nature of the irAE (including type, timing and Common Terminology Criteria for Adverse Events V5.0 CTCAE grade), and management strategies were collected from electronic patient records. Results The cohort included patients with a range of malignancies, most commonly melanoma (12 patients, 44%) and renal cell carcinoma (7 patients, 26%). Within the first 12 months of commencing an ICI, 81% of patients had developed a rheumatological irAE, with median time of onset being 4.1 months. The commonest ICI was pembrolizumab (13 patients, 48%). Inflammatory arthritis was the predominant irAE, affecting 61% of the cohort, followed by inflammatory myositis (22%), polymyalgia rheumatica (11%), large-vessel vasculitis (3%) and HLH (3%). First-line treatment with glucocorticoid monotherapy was initiated for all patients; however, almost a quarter required escalation to conventional disease-modifying antirheumatic drugs (csDMARDs), most commonly sulfasalazine. Importantly, 3 patients were escalated to biological DMARDs due to persistent or relapsing disease activity. Of those escalated to csDMARDs and biological DMARDs, half were able to continue ICI therapy. Fourteen patients (51%) from the overall cohort required complete cessation of ICI treatment due to grade 2 and 3 adverse events. Conclusion Rheumatological irAEs represent a substantial clinical challenge in cancer immunotherapy. Our real-world experience demonstrates that inflammatory arthritis is the most frequent presentation, usually arising within the first year of ICI treatment. Although many patients respond to a glucocorticoid monotherapy tapering regime, a significant minority required escalation to DMARDs. This underscores the need for an evidence-based treatment paradigm in this cohort, with potential for initiating DMARDs earlier to minimise toxicity from cumulative steroid burden. The findings also highlight the importance of rapid-access rheumatology services in optimising outcomes, including balancing effective irAE management with oncological treatment decisions in a multidisciplinary setting. Prospective studies are warranted to refine therapeutic strategies and better predict which patients are at risk of severe or refractory rheumatological irAEs, thus promoting personalised and targeted care. Disclosure J. Yuan-Dore: None. L. Kostanjsek: None. H. Spencer: None. S. Kesavan: None. T. Malley: None.