The knowledge and skills required for the onco-rheumatologist: Study of four-year consultation records of a high-volume cancer centre.

Objectives: Onco-rheumatology, the intersection of oncology and rheumatology, is an emerging field requiring further definition. This study aimed to identify the knowledge and skills essential for rheumatologists in clinical oncology.

Methods: We retrospectively reviewed consultations with the onco-rheumatology department of a high-volume tertiary cancer centre in Japan from January 2020 to December 2023.

Results: We analysed 417 consultations. The most common consultation (229, 55%) was related to immune checkpoint inhibitor-induced immune-related adverse events (irAEs). Of the 238 irAEs in 185 patients, 15% were rheumatic and 85% were non-rheumatic (e.g., hepatobiliary toxicities, colitis). Approximately 25% of non-endocrine irAEs were refractory/relapsing, requiring second-line therapy (e.g., mycophenolate mofetil, biologics, immunoglobulin). In addition to irAE consultations, 137 (33%) consultations were about possible rheumatic diseases. The final diagnosis often related to cancer treatment, such as granulocyte colony-stimulating factor-related aortitis (15 patients, 11%), olaparib-related erythema nodosum (10 patients, 7.3%), and surgical menopause-related arthralgia (10 patients, 7.3%). Five patients (3.6%) were diagnosed with autoinflammatory bone disease mimicking bone tumours.

Conclusions: Onco-rheumatologists are expected to play a central role in the management of a wide range of irAEs, not limited to rheumatic irAEs. They must also manage rheumatologic manifestations during cancer treatment and rheumatic diseases that mimic tumours.