title: Irritable bowel syndrome and risk of colorectal cancer: a Danish nationwide cohort study.
abstract: BACKGROUND
  Little is known about the risk of colorectal cancer among patients with irritable bowel syndrome (IBS).
  
  
  METHODS
  We conducted a nationwide cohort study using data from the Danish National Registry of Patients and the Danish Cancer Registry from 1977 to 2008. We included patients with a first-time hospital contact for IBS and followed them for colorectal cancer. We estimated the expected number of cancers by applying national rates and we computed standardised incidence ratios (SIRs) by comparing the observed number of colorectal cancers with the expected number. We stratified the SIRs according to age, gender, and time of follow-up.
  
  
  RESULTS
  Among 57,851 IBS patients, we identified 407 cases of colon cancer during a combined follow-up of 506,930 years (SIR, 1.14 (95% confidence interval (CI): 1.03-1.25) and 115 cases of rectal cancer, corresponding to a SIR of 0.67 (95% CI: 0.52-0.85). In the first 3 months after an IBS diagnosis, the SIR was 8.42 (95% CI: 6.48-10.75) for colon cancer and 4.81 (95% CI: 2.85-7.60) for rectal cancer. Thereafter, the SIRs declined and 4-10 years after an IBS diagnosis, the SIRs for both colon and rectal cancer remained below 0.95.
  
  
  CONCLUSIONS
  We found a decreased risk of colorectal cancer in the period 1-10 years after an IBS diagnosis. However, in the first 3 months after an IBS diagnosis, the risk of colon cancer was more than eight-fold increased and the risk of rectal cancer was five-fold increased. These increased risks are likely to be explained by diagnostic confusion because of overlapping symptomatology.
authors.affiliation: Department of Clinical Epidemiology, Clinical Institute, Aarhus University Hospital, Sdr. Skovvej 15, DK-9000, Aalborg, Denmark. m.noergaard@rn.dk
authors.forename: M
authors.initials: M
authors.lastname: Nørgaard
authors.forename: D K
authors.initials: DK
authors.lastname: Farkas
authors.forename: L
authors.initials: L
authors.lastname: Pedersen
authors.forename: R
authors.initials: R
authors.lastname: Erichsen
authors.forename: Z D
authors.initials: ZD
authors.lastname: de la Cour
authors.forename: H
authors.initials: H
authors.lastname: Gregersen
authors.forename: H T
authors.initials: HT
authors.lastname: Sørensen
mesh_terms: D000328:Adult; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000209:etiology*; D016001:Confidence Intervals; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D043183:Irritable Bowel Syndrome / Q000150:complications*; D008297:Male; D008875:Middle Aged; D012042:Registries; D012306:Risk