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Original article
Interval cancers in a FOBT-based colorectal cancer population screening programme: implications for stage, gender and tumour site
  1. R J C Steele1,2,
  2. P McClements3,
  3. C Watling3,
  4. G Libby2,
  5. D Weller4,
  6. D H Brewster3,
  7. R Black3,
  8. F A Carey5,
  9. C G Fraser2
  1. 1Department of Surgery, University of Dundee, Dundee, UK
  2. 2Scottish Bowel Screening Centre, King's Cross Hospital, Dundee, Dundee, UK
  3. 3Information Services, National Services Scotland, UK
  4. 4Centre for Population Health Sciences, University of Edinburgh, Edinburgh, UK
  5. 5Department of Pathology, University of Dundee, Dundee, UK
  1. Correspondence to Professor R J C Steele, Department of Surgery and Molecular Oncology, Level 6, Ninewells Hospital and Medical School, Dundee, DD1 9 SY, UK; r.j.c.steele{at}


Background Between 2000 and 2007, a demonstration pilot of biennial guaiac faecal occult blood test (GFOBT) screening was carried out in Scotland.

Methods Interval cancers were defined as cancers diagnosed within 2 years (ie, a complete screening round) of a negative GFOBT. The stage and outcome of the interval cancers were compared with those arising contemporaneously in the non-screened Scottish population. In addition, the gender and site distributions of the interval cancers were compared with those in the screen-detected group and the non-screened population.

Results Of the cancers diagnosed in the screened population, interval cancers comprised 31.2% in the first round, 47.7% in the second, and 58.9% in the third, although this was due to a decline in the numbers of screen-detected cancers rather than an increase in interval cancers. There were no consistent differences in the stage distribution of interval cancers and cancers from the non-screened population, and, in all three rounds, both overall and cancer-specific survival were significantly better for patients diagnosed with interval cancers (p<0.01). The percentage of cancers arising in women was significantly higher in the interval cancer group (50.2%) than in either the screen-detected group (35.3%, p<0.001) or the non-screened group (40.6%, p<0.001). In addition, the proportion of both right-sided and rectal cancers was significantly higher in the interval cancer group than in either the screen-detected (p<0.001) or non-screened (p<0.004) groups.

Conclusions Although GFOBT screening is associated with substantial interval cancer rates that increase with screening round, the absolute numbers do not. Interval cancers are associated with a better prognosis than cancers arising in a non-screened population, and GFOBT appears to preferentially detect cancers in men and the left side of the colon at the expense of cancers in women and in the right colon and rectum.

  • Colorectal cancer
  • screening
  • cancer registries
  • cancer epidemiology
  • cancer prevention
  • colorectal adenomas
  • colorectal carcinoma
  • Helicobacter pylori
  • acid-related diseases
  • non-ulcer dyspepsia
  • genetic polymorphisms
  • gastric neoplasia
  • colorectal cancer genes
  • microsatellite instability
  • cell cycle
  • gastrointestinal neoplasia
  • molecular pathology
  • screening

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  • The STROBE checklist has been used in the preparation of this document.

  • Funding The pilot was funded by the Scottish Government Health Department and the analysis was supported by a grant from the Chief Scientist Office (grant No CZH/6/4), Scottish Government Health Department to establish a Bowel Screening Research Unit. The University of Dundee acts as the sponsor, and administers the grant that supports the unit. All authors are independent of the funders in terms of freedom to publish.

  • Competing interests None.

  • Ethics approval Ethics approval was not sought for the demonstration pilot. This was a decision made by the UK National Screening Committee and endorsed by the UK Departments of Health on the grounds that screening for colorectal cancer using faecal occult blood is of proved efficacy, and the study constituted evaluation of the feasibility of introducing a screening programme into the NHS. Permission to access and analyse the anonymised data presented in this paper was granted by the Community Health Index Advisory Board and the Privacy Advisory Committee, National Services Scotland.

  • Provenance and peer review Not commissioned; externally peer reviewed.