Aim To investigate whether any patient or treatment characteristics are associated with the development of rheumatic immune‐related adverse events (irAEs) following programmed cell death protein 1 (PD‐1) inhibitor therapy for cancer. Method This was a retrospective chart review of all patients who were dispensed nivolumab or pembrolizumab at a single center before 1 January, 2017, with follow‐up until 1 July, 2017. Patients with any diagnosis of a non‐cutaneous irAE were identified, regardless of severity, and rheumatic irAEs were characterized. Results Of 244 episodes of therapy, a non‐cutaneous irAE occurred in 72 (29.5%). Rheumatic irAEs were diagnosed in 19 episodes of therapy (7.8%), with 12 de novo diagnoses (5.1% of episodes without a pre‐existing autoimmune rheumatic disease) and 7 exacerbations of existing disease. Review by a rheumatologist occurred in only 11 of these. Rheumatic irAEs were more common in patients with a good oncological response to therapy (relative risk [RR] 11.16), those being treated for melanoma (RR 2.94) and those who developed another non‐cutaneous irAE (RR 2.64). Conclusion Rheumatic irAEs are relatively common with PD‐1 inhibitor therapy, and appear to be associated with a good oncological response to therapy. Many rheumatic irAEs were not referred to rheumatological services. Prospective systematic investigation would be of benefit to explore these characteristics.

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