This study aims to investigate the prevalence and predictive risk factors of malignancy in patients with polymyositis (PM) and dermatomyositis (DM). The medical records of 192 PM/DM patients followed up in a medical center between January 2000 and December 2013 were reviewed. Among the 192 patients, 33 patients (17.2 %) had associated cancer. Both PM and DM are significantly associated with cancer, although the risk of cancer appears to be somewhat higher among patients with DM (23.0 %) than among those with PM (8.9 %). Nasopharyngeal cancer (30.3 %) and breast cancer (18.2 %) comprised the most common malignant diseases associated with PM/DM. Univariate analysis showed that an older age at PM/DM onset, heliotrope rash, Gottron's sign, dysphagia, and low creatine phosphokinase (CPK) level were associated with increased malignancy. Multivariate analysis revealed that independent predictors of malignancy in PM/DM were age >40 years at PM/DM onset (adjusted OR 3.44; 95 % CI 1.08-10.98; p = 0.037) and heliotrope rash (adjusted OR 2.96; 95 % CI 1.04-8.43; p = 0.042). During the follow-up period, 66 (34.4 %) patients died and the overall patient survival rates were 83.1 % at 1 year, 78.9 % at 2 years, 74.2 % at 5 years, and 65.5 % at 10 years. This study demonstrates a high frequency of malignancy (17.2 %) in DM/PM patients. Nasopharyngeal cancer and breast cancer were the most common cancer types in DM/PM patients in our study. Cancer screening should be offered to patients with newly diagnosed DM/PM. Moreover, all patients should be evaluated for the possibility of an underlying malignancy during treatment.
Keywords: Age; Dermatomyositis; Malignancy; Polymyositis; Risk factors.