title: The incidence of colorectal cancer following a negative screening sigmoidoscopy: implications for screening interval.
abstract: OBJECTIVE
  Current guidelines recommend a 5-year interval for colorectal cancer (CRC) screening by sigmoidoscopy. However, the optimal screening interval is uncertain. We estimated the annual incidence of distal and proximal CRC in the first 5 years following a negative sigmoidoscopy examination to gauge the potential benefit of rescreening in <5 years.
  
  
  METHODS
  A cohort of 72,483 participants in the Colon Cancer Prevention program of Kaiser Permanente of Northern California (KP) was defined using computerized databases. Men and women aged 50 years and older who had a negative screening flexible sigmoidoscopy examination between 1994 and 1996 and were considered not to be at high risk for developing CRC were included. Subjects were censored at the time of diagnosis (for cases), death, termination of KP membership, or subsequent colon examination.
  
  
  RESULTS
  Thirty cases of distal and 80 cases of proximal CRC occurred. Age-adjusted incidence rates of distal CRC ranged from a low of 2.8 per 100,000 person-years in the first year of follow-up to a high of 13.0 per 100,000 in the fourth year (rate difference, 10.2; 95% confidence interval, 1.1-19.3). However, for the entire follow-up period, incidence of distal CRC remained much lower than age-adjusted rates of 70.6 in the general population (Surveillance, Epidemiology, and End Results registry). The incidence of proximal CRC was also decreased modestly over population rates of disease.
  
  
  CONCLUSIONS
  Screening by sigmoidoscopy more frequently than every 5 years would likely lead, at best, to only modest improvements as compared with a 5-year screening interval.
authors.affiliation: Department of Epidemiology, University of Washington, Seattle, Washington, USA. pdoriaro@fhcrc.org
authors.forename: V Paul
authors.initials: VP
authors.lastname: Doria-Rose
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Levin
authors.forename: Joe V
authors.initials: JV
authors.lastname: Selby
authors.forename: Polly A
authors.initials: PA
authors.lastname: Newcomb
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Richert-Boe
authors.forename: Noel S
authors.initials: NS
authors.lastname: Weiss
mesh_terms: D000368:Aged; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D012812:Sigmoidoscopy / Q000379:methods*; D013997:Time Factors