Saturday, 10 June 2017

Screening interval and neoplasia detection rates according to the site distribution

Evidence from randomised trials indicates that annual guaiac FOBT is associated with a higher mortality reduction compared to biennial screening. Observational studies (Saito et al. 1995; Zappa et al. 2001) support the indication of biennial screening with iFOBT (see also Chapter 4). The recommended interval for colonoscopy screening is usually 10 years, although evidence from observational studies would indicate that the protective effect may be longer. A five-year interval is usually recommended for FS screening, although available evidence does not support such a recommendation: observational studies have indeed suggested that the protective effect of the exam for CRC arising in the distal colon may last for more than 10 years and it would justify the adoption of a protocol offering the test once in a lifetime (Selby et al. 1992; Newcomb et al. 2003).

The expected impact of endoscopic tests is also related to the site distribution of the neoplastic lesions in the colon and on their natural history

According to the results of a population-based case–control study, about 75–80% of colorectal cancer cases could be prevented by colonoscopy, with stronger effect for distal than for proximal CRCs (Brenner et al. 2007a). Recent cohort studies of people examined with colonoscopy confirm a protective effect of colonoscopy but suggest that the protective effect for proximal lesions might be overestimated 


Available evidence from cost-effectiveness analysis suggests that all commonly considered CRC screening strategies (FOBT, FlexiSig, TC total colonoscopy) are nearly equivalent for prevention of colorectal cancer mortality (assuming 100% adherence) (Zauber et al. 2008) and they therefore represent reasonable alternatives. Compared with no screening, nearly all analyses found that any of the common screening strategies for adults 50 years of age or older will reduce mortality from colorectal cancer. The cost per life-year saved for colorectal cancer screening (US$ 10 000 to US$ 25 000 for most strategies compared with no screening) compares favourably with other commonly endorsed preventive health care interventions, such as screening mammography for women older than 50 years of age or treatment of moderate hypertension.

The costs of a screening programme are strongly affected by the organisation of screening, including the costs of infrastructure, information technology, screening promotion, training and quality assurance, and by the characteristics of the health system. These same factors represent the main determinants of the cost of the screening test, which influences the estimates of the relative costs of different strategies. The timing of the costs and benefits should be considered as well: for example, endoscopy costs are met at the beginning, while those of FOBT spread over 10 years. 

Also, the advantage in terms of risk reduction must be weighed not only against the programme costs, but also against the inconvenience for the patient and the adverse effects (some of them causing death, potentially, thus mortality evaluation is also key in cost-effectiveness) associated with each strategy. These factors will influence the likelihood that patients will actually complete the tests required for any given strategy and therefore these factors also have a strong impact on the costs of the tests. 

Resources and sustainability of the programme  
A recent resources-use analysis of the strategies considered for the UK bowel cancer screening programmes found considerable differences between screening strategies in terms of endoscopy staffing and capital requirements. Limited availability of endoscopy services would favour the adoption of strategies using highly specific tests targeting older age groups, while a sigmoidoscopy-based strategy would be preferred if the financial resources are constrained. Also, the high number of cases detected when adopting a strategy using biennial FOBT for people aged 50 to 69 would have a significant impact on surgical services. Resource constraints, mainly related to availability of highly qualified personnel (Vijan et al. 2004) represent a strong barrier to the adoption of colonoscopy as a primary screening tool.

Summary of evidence 

  •  The balance in favour of screening is likely to be reached at rather different ages in the various European countries, and several years later among women than among men (III). 
  •  Offering people the option to choose a preferred strategy based on individual preferences and values does not result in increased coverage (II). 
  • Offering an alternative test to people refusing the main screening strategy adopted by a screening programme might represent a feasible and effective option (V). 
  •  The relative effectiveness in terms of incidence and mortality reduction of TC compared to FS might be overestimated (IV). 
  •  The costs of a screening programme are strongly affected by the organisation of screening, by the characteristics of the health system. Different strategies involve different timing of the expected costs and of the achievable benefits (III). 
  •  The impact of each specific strategy is strongly affected by its acceptability in the target population (III). 


  •  Gender- and age-specific screening schedules deserve careful attention in the design and implementation of screening interventions (III - C).
  •  The costs of screening organisation (including infrastructure, information technology, screening promotion, training and quality assurance), the incidence of adverse effects and the likelihood that patients will actually complete the tests required for any given strategy represent additional important factors to be taken into account in the design and implementation of screening interventions and in the choice of the screening strategy (III - A).

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