title: The lifelong risk of metachronous colorectal cancer justifies long-term colonoscopic follow-up.
abstract: BACKGROUND
  The aim of this study was to calculate the risk of metachronous colorectal cancers, to specify their characteristics and potential risk factors in a well-defined French population over a 27-year period.
  
  
  METHODS
  The 10,801 patients who had colorectal cancers totalled 61,879 person-years of follow-up. The actuarial method was used to obtain crude metachronous colorectal cancer rates. Standardised incidence ratios (SIRs) were calculated.
  
  
  RESULTS
  The cumulative rate of metachronous colorectal cancer was 1.8% at 5 years, 3.4% at 10 years and 7.2% at 20 years. The incidence of metachronous colorectal cancer following a first colorectal cancer was higher than expected (SIR: 1.5 [1.3-1.7] p<0.001). It remained greater throughout the study period, significantly only between the first and the fifth years following diagnosis (SIR: 1.9 [1.6-2.3] p<0.010). As compared to solitary cancers, metachronous cancers were diagnosed at earlier stages (23.5% versus 40.9% were stage I, p<0.001). None of the personal and tumour characteristics were predicting factors for the development of metachronous colorectal cancer.
  
  
  CONCLUSIONS
  Patients with colorectal cancer are at greater risk of developing a metachronous colorectal cancer. Among them, no predicting factors for the development of metachronous tumours were found. Thus lifelong colonoscopic surveillance is needed.
authors.affiliation: Inserm U866, Registre Bourguignon des Cancers Digestifs, Dijon, F-21079, France. anne-marie.bouvier@u-bourgogne.fr
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Bouvier
authors.forename: Marianne
authors.initials: M
authors.lastname: Latournerie
authors.forename: Valerie
authors.initials: V
authors.lastname: Jooste
authors.forename: Côme
authors.initials: C
authors.lastname: Lepage
authors.forename: Vanessa
authors.initials: V
authors.lastname: Cottet
authors.forename: Jean
authors.initials: J
authors.lastname: Faivre
mesh_terms: D000368:Aged; D003113:Colonoscopy / Q000379:methods*; D015179:Colorectal Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D004812:Epidemiologic Methods; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D008297:Male; D016609:Neoplasms, Second Primary / Q000175:diagnosis / Q000453:epidemiology*