Polymyositis/dermatomyositis and Malignancy Risk: A Metaanalysis Study

OBJECTIVE: To investigate the association between polymyositis (PM)/dermatomyositis (DM) and risks of malignancy. METHODS: We searched Pubmed for articles dated before August 16, 2013. Studies were included if they met the following criteria: (1) a cohort or observational study; (2) PM or DM as one of the exposures of interest; (3) cancer as an outcome of interest; and (4) the rate ratio (RR) or standardized incidence ratio (SIR) were available with their 95% CI. We used random-effects or fixed-effects models to calculate the pooled RR according to the heterogeneity test. RESULTS: Twenty publications were included. Compared with the general population, the pooled RR for patients with PM, DM, and PM/DM were 1.62 (95% CI 1.19-2.04), 5.50 (4.31-6.70), and 4.07 (3.02-5.12), respectively. The increased risks were more significant in patients within the first year of myositis diagnosis, male patients, and population-based studies (for DM). A significant association was also found between PM or DM and most site-specific malignancies. However, both PM and DM were not associated with stomach and prostate cancers. Significant heterogeneity was found between studies on association between PM/DM and overall malignancy, but not between PM/DM and the majority of site-specific malignancies, suggesting that that inherent malignancy difference may be a major source of heterogeneity. CONCLUSION: The present metaanalysis indicates that PM and DM are significantly associated with increased risks of overall malignancy and most site-specific malignancies. The number of studies on association between PM or DM and some malignancies is too small to draw a firm conclusion. Accordingly, more research is needed for these malignancies.