Incidence and predictive factors for malignancies in 136 Japanese patients with dermatomyositis, polymyositis and clinically amyopathic dermatomyositis

The aim of this study was to define the standardized incidence ratio (SIR) of malignancy and the potential risk factors of concomitant malignancies in patients with inflammatory myopathies, including clinically amyopathic dermatomyositis (CADM). A total of 145 patients diagnosed with either dermatomyositis/polymyositis (DM/PM) or CADM at our institute between 1984 and 2002 were enrolled in the study. The demographic, clinical and laboratory features of the patients at the time of DM/PM or CADM diagnosis were compared between patients with and without malignancies, respectively. Multivariate analysis by logistic regression was used to determine the independent risk factors for the development of malignancies in DM/PM patients. Malignancy was found in 17 of 70 patients with DM (24%), three of 15 patients with CADM (20%), and three of 51 patients with PM (6%). Gastric cancer (8/23) was the most common malignancy. Compared with general population, the SIR of malignancies was 13.8 (range 9.0–21.1). The patients who developed malignancies were older (61.5 vs. 51.1 years; P < 0.005), presented more often with dysphagia (61 vs. 15%; P < 0.0001) and were less likely to have the complication of interstitial lung disease (30 vs. 60%; P < 0.05). These features were independent predictive factors for developing malignancies in multiple logistic regression analysis. The results of our study confirm that CADM in addition to DM was associated with high rates of malignancy among our patient cohort.