Factors for malignancy in dermatomyositis and polymyositis: focusing on clinical and histopathologic aspects

Objective: Idiopathic inflammatory myopathies (IIMs) are associated with an increased risk of malignancy, underscoring the importance of appropriate cancer screening.This study aimed to evaluate the incidence of malignancy in patients with IIMs and identify associated clinical factors.Methods: We reviewed patients with IIMs who underwent muscle biopsy between 2000 and 2017.Malignancies diagnosed before or after IIM onset were identified.Malignancy-free survival was estimated using Kaplan-Meier analysis.Factors associated with ever-malignancy were analyzed using multivariable logistic regression, and independent factors associated with malignancy after IIM diagnosis were identified using Cox proportional hazards regression.Results: Of 129 patients with IIM, 29 (22.5%) had a malignancy before or after IIM diagnosis.On multivariable logistic regression, older age at diagnosis (odds ratio [OR] 1.07 per year) and dysphagia (OR 5.06) were independently associated with higher odds of ever-malignancy, whereas higher lactate dehydrogenase (LDH) levels (OR 0.99 per 10 U/L) and CD68 expression in inflammatory cells (OR 0.34) were associated with lower odds (all p<0.05).Among the 116 patients without malignancy at IIM diagnosis, older age (hazard ratio [HR] 1.08 per year), dysphagia (HR 6.30), and higher LDH levels (HR 0.99 per 10 U/L) were independently associated with incident malignancy on Cox regression, with 3-and 5-year malignancy-free survival rates of 90.6% and 81.0%, respectively.Conclusion: Malignancies may develop even after thorough initial screening at IIM diagnosis.Continued malignancy surveillance should be considered, particularly in older patients and those with dysphagia or lower LDH levels at diagnosis.