title: Increased risk of colorectal cancer after obesity surgery.
abstract: OBJECTIVE
  The purpose was to determine whether obesity surgery is associated with a long-term increased risk of colorectal cancer.
  
  
  BACKGROUND
  Long-term cancer risk after obesity surgery is not well characterized. Preliminary epidemiological observations and human tissue biomarker studies recently suggested an increased risk of colorectal cancer after obesity surgery.
  
  
  METHODS
  A nationwide retrospective register-based cohort study in Sweden was conducted in 1980-2009. The long-term risk of colorectal cancer in patients who underwent obesity surgery, and in an obese no surgery cohort, was compared with that of the age-, sex- and calendar year-matched general background population between 1980 and 2009. Obese individuals were stratified into an obesity surgery cohort and an obese no surgery cohort. The standardized incidence ratio (SIR), with 95% confidence interval (CI), was calculated.
  
  
  RESULTS
  Of 77,111 obese patients, 15,095 constituted the obesity surgery cohort and 62,016 constituted the obese no surgery cohort. In the obesity surgery cohort, we observed 70 patients with colorectal cancer, rendering an overall SIR of 1.60 (95% CI 1.25-2.02). The SIR for colorectal cancer increased with length of time after surgery, with a SIR of 2.00 (95% CI 1.48-2.64) after 10 years or more. In contrast, the overall SIR in the obese no surgery cohort (containing 373 colorectal cancers) was 1.26 (95% CI 1.14-1.40) and remained stable with increasing follow-up time.
  
  
  CONCLUSIONS
  Obesity surgery seems to be associated with an increased risk of colorectal cancer over time. These findings would prompt evaluation of colonoscopy surveillance for the increasingly large population who undergo obesity surgery.
authors.affiliation: *Upper Gastrointestinal Research, Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden †Leeds Institute of Molecular Medicine, Wellcome Trust Brenner Building, St James's University Hospital, Leeds, United Kingdom ‡Division of Cancer Studies, King's College London, London, United Kingdom.
authors.forename: Maryam
authors.initials: M
authors.lastname: Derogar
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hull
authors.forename: Prashant
authors.initials: P
authors.lastname: Kant
authors.forename: Magdalena
authors.initials: M
authors.lastname: Östlund
authors.forename: Yunxia
authors.initials: Y
authors.lastname: Lu
authors.forename: Jesper
authors.initials: J
authors.lastname: Lagergren
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000601:surgery*; D011183:Postoperative Complications / Q000453:epidemiology*; D012189:Retrospective Studies; D018570:Risk Assessment; D055815:Young Adult