title: Risk of multiple myeloma in rheumatoid arthritis: a meta-analysis of case-control and cohort studies.
abstract: OBJECTIVE
  multiple myeloma is a malignant neoplasm of plasma cells mainly affecting elderly patients. Despite the wealth of information available on therapeutic strategies, the etiology and pathogenesis of myeloma remain unclear. In the current study, a meta-analysis was conducted to assess the possible association between rheumatoid arthritis and myeloma.
  
  
  METHODS
  a literature search was conducted with PubMed, EMBASE and Web of Science for relevant studies published by December 25, 2013. Additionally, we searched annual meeting abstracts of the American Society of Hematology from 2004 to 2013. Only original studies that investigated the association between rheumatoid arthritis and myeloma were included. In total, 8 case-control and 10 cohort studies were identified for analysis.
  
  
  RESULTS
  the meta-estimate of the association between rheumatoid arthritis and myeloma was 1.14 (95% CI, 0.97-1.33) overall, with significant heterogeneity among studies. The relationship between myeloma and other autoimmune diseases was additionally examined from available data. Our results showed that myeloma risk is increased 1.31 to 1.65-fold in pernicious anemia and 1.36 to 2.30-fold in ankylosing spondylitis patients.
  
  
  CONCLUSIONS
  Rheumatoid arthritis does not appear to alter the risk of myeloma, while between-study heterogeneity analyses suggest caution in the interpretation of results. Pernicious anemia and ankylosing spondylitis may be potential risk factors for myeloma development. Future large-scale epidemiological studies with reliable exposure biomarkers are necessary to establish the possible contribution of autoimmune disorders to multiple myeloma.
authors.affiliation: Department of Hematology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China.
authors.forename: Kaini
authors.initials: K
authors.lastname: Shen
authors.affiliation: Zhejiang University, School of Medicine, Hangzhou, Zhejiang, People's Republic of China.
authors.forename: Gufeng
authors.initials: G
authors.lastname: Xu
authors.affiliation: Division of Health Sciences Research, Mayo Clinic, Scottsdale, Arizona, United States of America.
authors.forename: Qing
authors.initials: Q
authors.lastname: Wu
authors.affiliation: Department of Hematology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China.
authors.forename: Daobin
authors.initials: D
authors.lastname: Zhou
authors.affiliation: Department of Hematology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China.
authors.forename: Jian
authors.initials: J
authors.lastname: Li
mesh_terms: D001172:Arthritis, Rheumatoid / Q000150:complications*; D001327:Autoimmune Diseases / Q000150:complications; D016022:Case-Control Studies; D015331:Cohort Studies; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D009101:Multiple Myeloma / Q000150:complications*; D012307:Risk Factors