Temporal relationship between idiopathic inflammatory myopathies and malignancies and its mortality: a nationwide population-based study.

Among IIM patients with malignancy, common sites of malignancy were different between the CAM and CNAM groups, and patients with CAM had poor prognosis compared with CNAM patients. Key Points • The malignancies commonly occurred in incident idiopathic inflammatory myopathy (IIM) patients, especially within 1 year before and after the initial IIM diagnosis. • Patients with malignancy had poor survival compared with patients without malignancy. • Among the IIM patients with malignancy, patients who developed malignancy within 3 years of IIM diagnosis (cancer-associated myositis, or CAM, group) showed higher mortality than cancer-not-associated myositis, CNAM group. • We also found that the common types of malignancy were different between the CAM and CNAM groups.