Incidence and risk of musculoskeletal and rheumatologic (MSK-R) immune-related adverse events (irAEs) in a large real-world cohort.

e23409 Background: Immunotherapy (IT) improves cancer outcomes but is associated with irAEs, including MSK-R toxicities, which occur in 5–10% of patients, predominantly as arthralgias arthralgia 38% were female stage IV: 11%) and other advanced solid tumors. During median follow-up of 14 months (CI: 6-34), 46 MSK-R irAEs were observed, including 23 events among patients receiving first-line IT. Incidence rates were higher in IT than non-IT group (0.09 vs 0.02 per 100 person-years; P < 0.05). Inflammatory arthritis accounted for most events (0.06 vs 0.01 per 100 person-years). The 24-month CIR of MSK-R irAEs was 2.3% with IT vs 0.6% in non-IT (log-rank P < 0.01; HR 7.1; P < 0.01). The 24-month CIR of inflammatory arthritis was 1.7% versus 0.2% (P < 0.01). Among inflammatory arthritis cases, 72% were CTCAE grade II–III; immunomodulatory therapy was used in 65%, mainly corticosteroids, with an 89% response rate. Conclusions: In this large real-world cohort, IT was associated with a substantially increased risk of MSK-R irAEs, driven primarily by inflammatory arthritis, although events were uncommon, consistent with prior reports. These toxicities often required immunosuppressive therapy and were associated with IT interruption or discontinuation, underscoring the need for multidisciplinary management.