title: Risk of lymphoid neoplasms in a Swedish population-based cohort of 337,437 patients undergoing appendectomy.
abstract: OBJECTIVE
  Appendectomy remains one of the most common surgical procedures, but possible long-term consequences for health and disease are incompletely investigated. The appendix forms part of the secondary lymphoid system and appendectomy has been associated with increased risks of hematolymphoproliferative malignancies in some studies.
  
  
  METHODS
  We examined the risk of lymphoid neoplasms in a large cohort of 337,437 appendectomised patients <60 years of age in Sweden 1975-2009. We estimated relative risks of non-Hodgkin lymphoma (NHL) and major subtypes, Hodgkin lymphoma (HL), chronic lymphocytic leukaemia (CLL), myeloma, and acute lymphoblastic leukaemia (ALL) versus the general population using standardised incidence ratios (SIRs) with 95% confidence intervals (CIs).
  
  
  RESULTS
  There was no increased risk of NHL (SIR = 0.97, 95%CI 0.88-1.06), major NHL subtypes, CLL (SIR = 0.87, 95%CI 0.70-1.06), myeloma (SIR = 1.14, 95%CI 0.96-1.33) or ALL (SIR = 1.10, 95%CI 0.80-1.47) following appendectomy. An increased risk of HL was observed among patients diagnosed with appendicitis (SIR = 1.29, 95%CI 1.07-1.54, p=0.007), especially individuals aged <20 years at surgery (SIR = 1.43, 95%CI 1.11-1.82), and for the nodular sclerosis subtype of HL (SIR = 1.55, 95%CI 1.01-2.27). A marginally increased risk of myeloma was noted among men, but the association was limited to the first few years of follow-up.
  
  
  CONCLUSIONS
  Appendectomy is not associated with any notable increase in risk of lymphoid neoplasms. A small increased risk of HL following appendicitis (rather than appendectomy per se) could reflect a true association, or shared susceptibility to infection/inflammation among individuals prone to develop HL. The association observed for myeloma may be explained by chance or surveillance bias.
authors.affiliation: a Division of Epidemiology , Institute of Environmental Medicine, Karolinska Institutet , Stockholm , Sweden ;
authors.forename: Mohammad
authors.initials: M
authors.lastname: Mohammadi
authors.affiliation: b Department of Medical Epidemiology and Biostatistics , Karolinska Institutet , Stockholm , Sweden ;
authors.forename: Huan
authors.initials: H
authors.lastname: Song
authors.affiliation: c Unit of Biostatistics, Division of Epidemiology , Institute of Environmental Medicine, Karolinska Institutet , Stockholm , Sweden ;
authors.forename: Yang
authors.initials: Y
authors.lastname: Cao
authors.affiliation: d Department of Medicine, Clinical Epidemiology Unit , Solna, Karolinska Institutet, Karolinska University Hospital , Stockholm , Sweden ;|e Department of Immunology, Genetics and Pathology , Uppsala University , Uppsala , Sweden ;
authors.forename: Ingrid
authors.initials: I
authors.lastname: Glimelius
authors.affiliation: d Department of Medicine, Clinical Epidemiology Unit , Solna, Karolinska Institutet, Karolinska University Hospital , Stockholm , Sweden ;
authors.forename: Anders
authors.initials: A
authors.lastname: Ekbom
authors.affiliation: b Department of Medical Epidemiology and Biostatistics , Karolinska Institutet , Stockholm , Sweden ;
authors.forename: Weimin
authors.initials: W
authors.lastname: Ye
authors.affiliation: d Department of Medicine, Clinical Epidemiology Unit , Solna, Karolinska Institutet, Karolinska University Hospital , Stockholm , Sweden ;|f Hematology Center , Karolinska University Hospital , Stockholm , Sweden.
authors.forename: Karin E
authors.initials: KE
authors.lastname: Smedby
mesh_terms: D000328:Adult; D001062:Appendectomy / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008223:Lymphoma / Q000453:epidemiology / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D012189:Retrospective Studies; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: Acute lymphoblastic leukaemia; Hodgkin lymphoma; appendectomy; appendicitis; chronic lymphocytic leukaemia; myeloma; non-Hodgkin lymphoma