Validation of the International Myositis Assessment and Clinical Studies Group guideline on cancer risk stratification

Adult-onset Idiopathic inflammatory myopathies (IIMs) are associated with cancer. Guideline on cancer risk stratifications and screening in IIM patients was recently published, but their external validity remains verified. We evaluated its applicability and reliability among a Hong Kong IIM cohort. The longitudinal observational cohort collected data from IIM patients fulfilling relevant classification criteria from 8 rheumatology centres in Hong Kong. Demographic, clinical and laboratory data were reviewed from 2004-2023. IIM patients were stratified into standard, intermediate or high-risk subgroups according to the IMACS guideline. The occurrence of malignancy at or after IIM diagnosis was analyzed. Independent risk factors for cancer were evaluated. 479 patients were included with 327 females (68.3%) and mean age of IIM diagnosis at 54.5 ± 13.6 years. 214 (44.7%) and 238 (49.7%) patients were stratified to high and intermediate risk groups, respectively. Only 5.6% belonged to the standard-risk group. 60 patients (12.5%) had cancer within 3 years of IIM diagnosis. Nasopharyngeal (25%), lung (21.1%) and breast (10.5%) were the top 3 cancers. Significantly more patients (44, 20.6%) in the high-risk group developed cancer within 3 years, compared with intermediate (6.7%, p< 0.001) and standard-risk (0%, p= 0.009) groups. Risk factors for cancer included older age (OR : 1.048, 95%CI : 1.019-1.078), Gottron's rash (OR : 2.453, 95%CI : 1.123-5.356), absence of ILD (OR 2.695, 95% CI : 1.154-6.295), anti-TIF1g positivity (OR : 4.627, 95% CI : 2.046-10.461) and anti-SAE1 positivity (OR : 5.325, 95% CI : 1.271-22.300). Our real-world study supported the accuracy of cancer risk stratification. Vast majority of IIM patients would be subjected to extensive cancer screening when the guideline was applied.