Risk of Malignancy in Dermatomyositis and Polymyositis: A Systematic Review and Meta-Analysis

Background: There is variation in the risk of malignancy in dermatomyositis (DM) and polymyositis (PM) in the existing literature. Objective: To conduct a meta-analysis to estimate the risk of malignancy in DM and PM as compared with the general population. Methods: Medline and Embase Database abstracts were searched through August 2014 using the search terms myositis, neoplasms, and paraneoplastic syndromes. Population-based, observational studies in English were included. Meta-analyses were conducted using random-effects models. Results: A total of 5 studies with 4538 DM or PM patients were included in the analysis. The overall relative risk was 4.66 for DM and 1.75 for PM. By gender, the standardized incidence ratio (SIR) of malignancy among DM patients was 5.29 for males and 4.56 for females; the SIR of malignancy among PM patients was 1.62 for males and 2.02 for females. By time since diagnosis, the SIR of malignancy among DM patients was 17.29 in the first year, 2.7 between 1 and 5 years, and 1.37 after 5 years. By age group, the SIR among DM patients was 2.79 for patients between 15 and 44 years and 3.13 beyond 45 years. Conclusions: Both DM and PM are associated with increased risk of malignancy, but the risk is higher in DM. The risk of malignancy is present in both genders and all age groups and is highest in the first year after diagnosis but persists beyond the fifth year in DM. Adults should be evaluated for malignancy at diagnosis, followed by long-term surveillance.