title: Interval cancers in a national colorectal cancer screening programme.
abstract: BACKGROUND
  Little is known about interval cancers (ICs) in colorectal cancer (CRC) screening.
  
  
  OBJECTIVE
  The purpose of this study was to identify IC characteristics and compare these with screen-detected cancers (SCs) and cancers in non-participants (NPCs) over the same time period.
  
  
  METHODS
  This was an observational study done in the first round of the Scottish Bowel Screening Programme. All individuals (772,790), aged 50-74 years, invited to participate between 1 January 2007 and 31 May 2009 were studied by linking their screening records with confirmed CRC records in the Scottish Cancer Registry (SCR). Characteristics of SC, IC and NPC were determined.
  
  
  RESULTS
  There were 555 SCs, 502 ICs and 922 NPCs. SCs were at an earlier stage than ICs and NPCs (33.9% Dukes' A as against 18.7% in IC and 11.3% in NPC), screening preferentially detected cancers in males (64.7% as against 52.8% in IC and 59.7% in NPC): this was independent of a different cancer site distribution in males and females. SC in the colon were less advanced than IC, but not in the rectum.
  
  
  CONCLUSIONS
  ICs account for 47.5% of the CRCs in the screened population, indicating approximately 50% screening test sensitivity: guaiac faecal occult blood testing (gFOBT) sensitivity is less for women than for men and gFOBT screening may not be effective for rectal cancer.
authors.affiliation: Centre for Research into Cancer Prevention and Screening (CRiPS), University of Dundee, Dundee, UK.
authors.forename: Robert Jc
authors.initials: RJ
authors.lastname: Steele
authors.affiliation: Information Services, National Services Scotland, Edinburgh, UK.
authors.forename: Greig
authors.initials: G
authors.lastname: Stanners
authors.affiliation: Information Services, National Services Scotland, Edinburgh, UK.
authors.forename: Jaroslaw
authors.initials: J
authors.lastname: Lang
authors.affiliation: Scottish Cancer Registry, Edinburgh, UK.
authors.forename: David H
authors.initials: DH
authors.lastname: Brewster
authors.affiliation: Department of Pathology, Ninewells Hospital and Medical School, Dundee, UK.
authors.forename: Francis A
authors.initials: FA
authors.lastname: Carey
authors.affiliation: Centre for Research into Cancer Prevention and Screening (CRiPS), University of Dundee, Dundee, UK.
authors.forename: Callum G
authors.initials: CG
authors.lastname: Fraser
keywords: Colorectal cancer screening; faecal occult blood test; interval cancer; non-participant cancer; screen-detected cancer