title: Risk of obesity-related cancer after obesity surgery in a population-based cohort study.
abstract: OBJECTIVE
  Obesity increases the risk of several cancers, but it is uncertain whether weight reduction is followed by any decreased risk. To address this topic, we selected a group of patients representing a substantial weight loss starting at a defined time, ie, patients submitted to obesity surgery. We hypothesized that risk of obesity-related cancer decreases with time after obesity surgery.
  
  
  BACKGROUND
  A nationwide, population-based cohort study of obesity surgery in 1980-2006 as registered in the Swedish Patient Register. New cancers were identified through the Swedish Cancer Register. Cohort members' observed total number of overall obesity-related cancers and groups of obesity-related cancer (breast, prostate, colorectal, endometrial, kidney) were divided by the expected numbers, representing the baseline risk, thus calculating standardized incidence ratios (SIRs) with 95% confidence intervals (CIs). Time trends of SIR after obesity surgery were the main outcome measure.
  
  
  RESULTS
  Among a total of 13,123 obesity surgery patients, contributing with 125,049 person-years of follow-up, 296 new cases of obesity-related cancer were identified. There was no overall decrease in SIR of obesity-related cancer with increased time after obesity surgery (P for trend 0.40). Similarly, no statistically significant trends with follow-up time were found for cancer of the breast (P = 0.60), prostate (P = 0.34), endometrium (P = 0.83), or kidney (P = 0.42), while the risk of colorectal cancer increased with time (P for trend 0.01) after obesity surgery.
  
  
  CONCLUSIONS
  The weight reduction following obesity surgery might not be entailed by a decreased risk of obesity-related cancer with increasing follow-up time as compared with the baseline risk.
authors.affiliation: Department of Molecular Medicine and Surgery, Upper Gastrointestinal Research, Karolinska Institutet, Stockholm, Sweden. magdalena.plecka-ostlund@sodersjukhuset.se
authors.forename: Magdalena Plecka
authors.initials: MP
authors.lastname: Ostlund
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; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000209:etiology*; D009765:Obesity / Q000150:complications / Q000601:surgery*; D012042:Registries; D012307:Risk Factors; D015431:Weight Loss; D055815:Young Adult