Performance and potential impact of the IMACS cancer screening guideline in myositis: analysis in a myositis referral centre.

Objectives: To evaluate the performance, direct costs and radiation exposure of the cancer screening strategy proposed by the International Myositis Assessment and Clinical Studies Group (IMACS) in patients with idiopathic inflammatory myopathies (IIMs) at a myositis referral centre compared with real-world cancer screening. Methods: This is a retrospective study involving consecutive patients registered in a single-centre prospective IIM database from 2014 to 2024 who had no cancer within 3 years before IIM diagnosis. The patients were stratified into high, moderate or standard risk of cancer according to the IMACS risk stratification model and cancer events were collected within 3 years following IIM diagnosis. Cancer detection rate, direct costs and radiation exposure associated with the IMACS screening strategy were estimated. Results: We included 183 patients with a median age at IIM onset of 61 years and 66.7% being female. The IMACS risk stratification model classified 75 (41.0%), 100 (54.6%) and 8 (4.4%) patients into high, moderate and standard risk, respectively. We identified 15 (20.0%), 8 (8.0%) and 0 cancer events in each risk group, respectively. The IMACS strategy could have identified 18/22 (81.8%) of the cancer events. Direct costs and radiation exposure associated with the IMACS strategy were estimated to be higher than our real-world practice, especially in the high- and moderate-risk groups. Conclusions: The IMACS IIM-associated cancer risk stratification model and screening strategy showed satisfactory performance in a single-centre IIM cohort, while most patients would be classified into the high- and moderate-risk groups, where enhanced cancer screening is recommended.