Risk factors for cancer‐associated myositis: A large‐scale multicenter cohort study

Abstract Aim The aim of this study was to identify the risk factors and prognosis of patients with cancer‐associated myositis (CAM). Method Four hundred and eighty‐seven patients with dermatomyositis (DM), clinical amyopathic dermatomyositis (CADM) and polymyositis (PM) from 3 clinical centers were enrolled retrospectively in this study. Clinical and laboratory data of CAM and non‐CAM patients were compared. Logistic regression analysis was used to identify risk factors of CAM. Results Out of the 487 patients with DM/CADM/PM, 7.0% (34/487) of patients were classified as CAM. Older age (53.91 ± 13.32 vs. 48.76 ± 14.34 years), heliotrope rash (61.8% vs. 41.9%), shawl sign (41.2% vs. 22.1%), V sign (58.8% vs. 38.6%) were observed significantly more commonly in patients with CAM than those without CAM (all P < .05). Fever (17.7% vs. 37.8%), arthralgia/arthritis (23.5% vs. 45.7%), interstitial lung disease (ILD, 38.2% vs 68.9%) were significantly less common in the CAM group than the non‐CAM group. Age at onset (odds ratio [OR] 1.036, 95% CI 1.001‐1.072, P = .042), shawl sign (OR 2.748, 95% CI 1.107‐6.822, P = .029), anti‐transition initiation factor (TIF)‐1γ antibody (OR 4.012, 95% CI 1.268‐12.687, P = .018) were identified as the initial risk factors for the onset of CAM, and ILD was identified as a protective factor for CAM (OR 0.292, 95% CI 0.115‐0.739, P = .009). All‐cause mortality was significantly higher in CAM patients compared with non‐CAM patients ( P = .001). Conclusion The mortality of patients with CAM was higher than DM/CADM/PM patients without cancer. Malignancy should be screened in DM/CADM/PM patients especially with risk factors, including older age, shawl sign, anti‐TIF‐1γ antibody, and lack of ILD.