DOI: 10.12809/hkmj177058
© Hong Kong Academy of Medicine. CC BY-NC-ND 4.0
COMMENTARY
Challenges to the adoption of risk algorithms for
colorectal cancer screening programmes: perspectives for future research
JJ Huang, MSc; Jason LW Huang, MD
The Jockey Club School of Public Health and Primary
Care, Faculty of Medicine, The Chinese University of Hong Kong, Shatin,
Hong Kong
Corresponding author: Dr Jason LW Huang (jasonlwhuang@link.cuhk.edu.hk)
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Colorectal cancer (CRC) is the third most common
cancer worldwide and accounts for 10% of all cancer new cases.1 There is concrete evidence for the effectiveness of
screening in reducing CRC-related mortality.2
In some developed nations such as the US, colonoscopy has been used as a
primary screening tool.3 Because
not all countries are equipped with adequate colonoscopy resources for
population-based screening, it is recommended for individuals with
increased risk for CRC only.4 Hence
in many countries, the concept of risk-based screening is gaining appeal,
particularly the use of scores to risk-stratify subjects and classify
screening participants as average-risk or high-risk. A prominent example
is the risk score devised and validated by the Asia-Pacific CRC working
group, named the Asia-Pacific Colorectal Screening (APCS) score.5 It uses age, gender, smoking habit, and presence of a
history of CRC in a first-degree relative to identify high-risk
individuals (score 4-7 out of 7) who are more likely to benefit from
colonoscopy screening due to the higher yield of advanced colorectal
neoplasia. Subjects who score 0-3 are advised to undertake faecal occult
blood tests. The APCS score has a high level of validity and was developed
following rigorous statistical analysis.6
Other validated risk scores have been constructed using similar methods
and have potential for use in clinical practice.7
8
Yeoh et al5
also identified some issues related to the application of the APCS score.
The objective of this commentary is to discuss the potential challenges
and perspectives for future research into risk-based CRC screening.
First, not all known risk factors for CRC can be
incorporated into the model due to practical difficulties. Some
information is difficult or too time-consuming to be accurately collected
in a clinic scenario, such as dietary habits and level of physical
activity. Second, increasing the number of variables will inevitably
reduce the practical utility of the scoring systems, and not all risk
factors possess good predictive value. This might explain why some scoring
systems suggest a need for further work,9
10 as several algorithms have
relatively modest concordance statistics, barely exceeding the acceptable
level of “satisfactory” (0.6-0.7). Furthermore, the derivation process of
these scoring systems usually employs a split-cohort strategy without
external validation. Subsequent validation in other populations might not
result in similar discriminatory capabilities.11
Third, there are concerns about the generalisability of these scores in
people residing in different regions around the world. It is well
recognised that the prevalence and distribution of advanced colorectal
neoplasia differ for different ethnicities. Fourth, in order for a local
government to use these risk scoring tools, their efficiency and
cost-effectiveness must be evaluated in the local context. Formal
cost-effectiveness analysis based on various risk factors should be
performed for each population to be served.12
13 14
There are also concerns about the acceptability and distributive justice
of such an approach. Whilst some unhealthy lifestyle habits such as
smoking, drinking alcohol, and consuming red meat are risk factors for
CRC, it is hard to justify why people ‘choosing these lifestyle habits’
deserve to be screened by a more expensive screening option such as
colonoscopy.
These risk scores are scientifically robust and
nicely constructed. Nonetheless, at the health care system level, their
generalisability remains uncertain. The different opinions of various
stakeholders also complicate matters—the perception of risk is subjective
and it is likely that screening participants will be destined to undergo
colonoscopy despite having an average risk as assessed by the risk scores,
not because they wish to.
Prior to 2016, there was no population-based CRC
screening programme in Hong Kong. In response to the increasing health
burden posed by CRC, the government has since launched a 3-year
subsidised, CRC screening pilot programme in the population for
asymptomatic individuals aged 61 to 70 years. The screening modality uses
a 2-yearly, two-specimen faecal immunochemical test, followed by
colonoscopy if any one sample is positive. This pilot programme collects
data on its feasibility and cost-effectiveness. It is yet to be discussed
whether a risk-based approach can be incorporated into future programmes.
We believe each country will need a screening
programme tailored to the characteristics of its own population.
Nonetheless, collaboration among specialist personnel may be helpful to
establish several initiatives. First, we need to enhance the
discriminatory capability of screening tests. Currently the predictive
variables are presented as categorical variables in most scoring systems
that are more user-friendly and more convenient. Appropriate statistical
adjustments could be made to obtain more precise weightings for each risk
factor, and this might increase the concordance statistics of the
algorithm.
Second, development of non-invasive biomarkers
affordable to the general public should be an important focus. There is
increasing evidence to support the use of newer modalities, such as
computed tomographic colonography and faecal DNA testing. These may serve
as useful tools in the screening of CRC.15
Despite the potential risk of radiation exposure, the benefits outweigh
potential harm when computed tomographic colonography is used in CRC
screening.16 A multi-target faecal
DNA test that detects circulating methylated septin 9 gene DNA has also
been approved for CRC screening.17
Magnetic resonance colonography and capsule endoscopy are mainly used for
diagnosis rather than screening.18
19 Although magnetic resonance
colonography does not expose the individual to radiation and requires no
sedation, use of intravenous contrast agent is required.20 Capsule endoscopy is non-invasive and also requires
no sedation but the bowel preparation is more complicated than that
required for colonoscopy.21 A
recent report showed that faecal quantification of Fusobacterium
nucleatum could be a useful supplement to faecal immunochemical test
in the diagnosis of CRC and advanced adenoma. This non-invasive approach
may improve the screening accuracy of current faecal immunochemical test.22
Third, effective education programmes for the
general public about the risk of CRC should be formulated. In order for
risk-based screening to be efficient, the effectiveness and sustainability
of health education about the various risk factors for CRC should be
enhanced in order to heighten community awareness.23 Acceptability, perception, attitude, and satisfaction
of risk-based screening should also be evaluated. Previous studies have
identified various barriers to CRC screening, including economic concerns,
limited access to screening services, screening-induced discomfort,
perceived bodily harm, embarrassment, and anxiety induced by screening.24 Individuals at high risk of CRC
who are targeted for screening should have their attitude and perception
identified in a systematic manner under a theoretical framework, such as
the health belief model.25
Lastly, cost-effectiveness analysis of competing
screening strategies in different patient groups should be performed in
different settings. This warrants further research funding, particularly
in population groups at high risk of CRC, including patients with medical
conditions such as non-alcoholic fatty liver disease, diabetes, and
metabolic syndrome.
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