Objectives To evaluate the prevalence and type of rheumatic immune-related adverse events (irAEs) in patients receiving immune checkpoint inhibitors (ICIs), as well as the correlation with tumour response.

Methods This was a single-centre prospective observational study including all cancer patients receiving ICIs. The occurrence of irAEs and tumour response was assessed on a regular basis. Patients who experienced musculoskeletal symptoms were referred to the department of rheumatology for clinical evaluation and management.

Results From September 2015 to May 2017, 524 patients received ICIs and 35 were referred to the department of rheumatology (6.6%). All but one of the rheumatic irAEs occurred with anti-programmed cell death protein 1(PD-1)/PD-1 ligand 1(PD-L1) antibodies, with a median exposure time of 70 days. There were two distinct clinical presentations: (1) inflammatory arthritis (3.8%) mimicking either rheumatoid arthritis (n=7), polymyalgia rheumatica (n=11) or psoriatic arthritis (n=2) and (2) non-inflammatory musculoskeletal conditions (2.8%; n=15). One patient with rheumatoid arthritis was anti-cyclic citrullinated peptide (anti-CCP) positive. Nineteen patients required glucocorticoids, and methotrexate was started in two patients. Non-inflammatory disorders were managed with non-steroidal anti-inflammatory drugs, analgesics and/or physiotherapy. ICI treatment was pursued in all but one patient. Patients with rheumatic irAEs had a higher tumour response rate compared with patients without irAEs (85.7% vs 35.3%; P<0.0001).

Conclusion Since ICIs are used with increasing frequency, knowledge of rheumatic irAEs and their management is of major interest. All patients were responsive either to low-to-moderate doses of prednisone or symptomatic therapies and did not require ICI discontinuation. Furthermore, tumour response was significantly higher in patients who experienced rheumatic irAEs.