Pre-planning is necessary, because good governance requires consensus-building.
Consensus building
National governance structures are necessary for evidence-based decisions on developing cancer screening programmes for new cancer sites. Well-functioning established programmes can also need modification and reorganization due to technological development or other changes.
Formulation of a screening policy proposal requires systematic evidence on the benefits and harms of screening. National prioritization can be based furthermore on projections on disease burden, on capacity and resource needs of quality-assured testing and treatment strategies, and on alternative or complementary prevention strategies such as primary prevention. Information on possible health inequalities, and possibilities to tackle them also need to be considered.
To build up consensus you need to:
- Acquire evidence and/or build evidence synthesis
- Assess baseline conditions and capacities
- Assess health economics and prioritization
- Start to develop communication strategy
Screening criteria
Several criteria need to be considered before implementing potential new programmes or modifying existing programmes. Here is a synthesis of emerging screening criteria proposed since 1968:
- Screening programme should respond to a recognized need
- Objectives of screening should be defined at the outset
- There should be a defined target population
- There should be scientific evidence of screening programme effectiveness
- Programme should integrate education, testing, clinical services and programme management
- There should be quality assurance, with mechanisms to minimize the potential risks of screening
- Programme should ensure informed choice, confidentiality and respect for autonomy
- Programme should promote equity and access to screening for the entire target population
- Programme evaluation should be planned from the outset
- Overall benefits of screening should outweigh the harm
Source: Andermann A et al. Revisiting Wilson and Jungner in the genomic age: a review of screening criteria over the past 40 years. Bulletin of the World Health Organization, 2008;86:317–319
Key criteria for new programmes
There are three key criteria for deciding whether a screening programme for any other primary site than those recommended nowadays (breast, cervix, colorectum) should be adopted:
- is there evidence for the effectiveness of screening?
- is there evidence that the benefits of screening outweigh the harms?
- is screening cost-effective?
Step 1: Effectiveness
The first step is to determine whether screening is effective, that is, does it reduce mortality from the target disease. This can only be done by means of randomized controlled trials (RCTs) with disease-specific mortality as the primary end-point and assessing all other important critical outcomes, incidental findings, and adverse effects. RCTs evaluating screening have to be large and follow-up has to be long. Screening trials are relatively expensive. Nevertheless, investments to RCTs are indispensable.
Limitations of RCTs
While randomized controlled trials (RCTs) are indispensable for evaluating screening, they have their limitations.
1. RCTs are relatively expensive and time consuming, limiting the number of RCTs that have evaluated screening.
2. RCTs usually have a limited accrual and follow-up time. As a result, they cannot be used to determine lifetime health effects and costs, which is necessary to directly determine the cost-effectiveness of screening. Therefore further simulations based on the trial results are needed prior decisions to start, and the real-life effectiveness and cost-effectiveness can be assessed only when the programme has been run already for a long enough time.
3. The effectiveness of screening might differ between settings. Sources for variation in the results include background risk, quality and costs of screening and management in a given health care system, use of services outside the screening programme and methods in the health-economical evaluation itself.
Decision models provide a useful tool to extrapolate evidence from RCTs and address the question of which screening strategy is optimal given local conditions, life expectancy, costs, resource availability and population preferences.
Step 2: Benefit-harm ratio
The second step is to determine whether the benefits of screening outweigh the harms. A frequently used method to value the health effects of screening is by using utility weights.
Possible benefits of a screening programme are;
- a reduction in disease-specific mortality or all-cause mortality
- a reduction of advanced disease and aggressive treatment
- quality- adjusted life-years (QALYs) gained.
Possible harms of screening are:
- pain and stress of the screen test and diagnosis
- false-positive tests results
- more life living with the knowledge of the disease
- false reassurance
- overdiagnosis
- overtreatment
- complications and other adverse events due to cancer treatments
