title: Cancer risk in dermatomyositis: a meta-analysis of cohort studies.
abstract: BACKGROUND
  An association between dermatomyositis (DM) and cancer has been reported since 1916; however, estimates of the associated risk vary widely. For cost-effectiveness reasons it might be important to elucidate the degree of overall cancer risk in DM.
  
  
  OBJECTIVE
  The aim of this systematic review was to investigate the association of cancer in DM by performing a meta-analysis of cohort studies.
  
  
  METHODS
  A systematic literature search of PubMed, Ovid MEDLINE, EMBASE, Web of Science, Scopus, and the Cochrane Collaboration was conducted without language restriction, to 1 May 2014.
  
  
  METHODS
  Inclusion criteria included cohort studies assessing overall cancer risk in DM. Two reviewers independently performed the study selection. Inter-rater reliability for inclusion decisions was quantified using Cohen's κ statistic. Disagreements were resolved by discussion.
  
  
  METHODS
  Desired variables were extracted from eligible studies independently by two investigators and disagreements were resolved by discussion. Quality of the selected studies was assessed using a modification of a recently employed system designed with reference to Meta-analysis Of Observational Studies in Epidemiology (MOOSE), Quality Assessment Tool for Systematic Reviews of Observational Studies (QATSO), and Strengthening the Reporting of Observational Studies in Epidemiology (STROBE). Summary estimates were derived using a random-effects model.
  
  
  METHODS
  Main outcome was the calculated relative risk of developing cancer after diagnosis of DM compared with the general population, estimated as the age- and sex-adjusted standardized incidence ratio (SIR). We hypothesized a priori that the relative risk would be higher in patients diagnosed with DM.
  
  
  RESULTS
  A total of 1,272 articles were initially identified but only ten studies met the inclusion criteria. Selected studies included seven population-based and three hospital-based DM cohorts that ranged from 49 to 1,012 patients and had mean follow-up times from 3.7 to 10.4 years. The pooled SIR for the incidence of overall cancer in DM patients was 4.79 (95% confidence interval 3.71-5.87) with significant heterogeneity (I(2) = 85.8%). However, the heterogeneity had no substantial influence on the pooled SIR for overall cancer in DM according to the sensitivity analysis.
  
  
  CONCLUSIONS
  Compared with the general population, DM patients are at a significantly increased risk for developing cancer. Understanding the magnitude of this risk is highly relevant toward assisting healthcare providers in clinical decision making, such as screening DM patients for cancer.
authors.affiliation: Mayo Graduate School, Mayo Clinic, 200 1st St SW, Rochester, MN, 55905, USA, olazagastilourido.jeannette@mayo.edu.
authors.forename: Jeannette M
authors.initials: JM
authors.lastname: Olazagasti
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Baez
authors.forename: David A
authors.initials: DA
authors.lastname: Wetter
authors.forename: Floranne C
authors.initials: FC
authors.lastname: Ernste
mesh_terms: D003882:Dermatomyositis / Q000150:complications*; D006801:Humans; D009369:Neoplasms / Q000209:etiology*; D018570:Risk Assessment; D012307:Risk Factors