title: Risk of Gastrointestinal Cancers among Patients with Appendectomy: A Large-Scale Swedish Register-Based Cohort Study during 1970-2009.
abstract: BACKGROUND
  Removal of the appendix might induce physiological changes in the gastrointestinal tract, and subsequently play a role in carcinogenesis. Therefore, we conducted a nationwide register-based cohort study in Sweden to investigate whether appendectomy is associated with altered risks of gastrointestinal cancers.
  
  
  METHODS
  A population-based cohort study was conducted using the Swedish national registries, including 480,382 eligible patients followed during the period of 1970-2009 for the occurrence of site-specific gastrointestinal cancer (esophageal/gastric/colon/rectal cancer). Outcome and censoring information was collected by linkage to health and demography registers. We examined the incidence of appendectomy in Sweden using data from 1987-2009. We also calculated standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) to estimate the relative gastrointestinal cancer risk through comparison to the general population.
  
  
  RESULTS
  We noted an overall decrease in the age-standardized incidence of appendectomy among the entire Swedish population from 189.3 to 105.6 per 100,000 individuals between 1987 and 2009. Grouped by different discharge diagnosis, acute appendicitis, incidental appendectomy, and entirely negative appendectomy continuously decreased over the study period, while the perforation ratio (18%-23%) stayed relatively constant. Compared to the general population, no excess cancer risk was observed for gastrointestinal cancers under study with the exception of a marginally elevated risk for esophageal adenocarcinoma (SIR 1.32, 95% CI 1.09-1.58).
  
  
  CONCLUSIONS
  In Sweden, the incidence of appendectomy and acute appendicitis has decreased during 1987-2009. No excess gastrointestinal cancer risks were observed among these appendectomized patients, with the possible exception of esophageal adenocarcinoma.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Huan
authors.initials: H
authors.lastname: Song
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, United States of America.
authors.forename: Christian C
authors.initials: CC
authors.lastname: Abnet
authors.affiliation: Department of Digestive Diseases, Karolinska University Hospital, Huddinge, Stockholm, Sweden.
authors.forename: Åke
authors.initials: Å
authors.lastname: Andrén-Sandberg
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, United States of America.
authors.forename: Anil K
authors.initials: AK
authors.lastname: Chaturvedi
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Weimin
authors.initials: W
authors.lastname: Ye
mesh_terms: D000293:Adolescent; D000328:Adult; D001062:Appendectomy / Q000009:adverse effects*; D001064:Appendicitis / Q000601:surgery; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D013548:Sweden; D055815:Young Adult