This is a plain English summary of an original research article
Bowel cancer, also known as colorectal cancer, is treatable and curable if caught early. NHS England’s Bowel Cancer Screening Programme aims to find warning signs in people aged 60 to 74.
They are invited to take a faecal immunochemical test (FIT) every two years. FIT measures blood in faeces and people with levels above a certain threshold are invited to have their bowel tissue examined for signs of cancer. Growths which could become cancerous (polyps) are removed and cancers prevented.
Researchers were surprised to find that the FIT threshold for further investigation is set at a point that may miss more than half of bowel cancer cases. This highlights a need to improve the NHS screening programme.
They suggest that the programme could make better use of FIT’s ability to provide the exact concentration of blood in faeces (rather than only whether it is above or below a cutoff level).
A new, multi-threshold strategy would mean referring people different follow-up according to their results. Screening intervals could be varied, and different ways of examining the bowel could be used (for example, sigmoidoscopy examines only the lower bowel). This could reduce the number of cancers missed while minimising the demand on services.
What’s the issue?
Bowel cancer affects the colon and rectum. It usually begins in clumps of cells called polyps on the inner lining of the bowel. Although some polyps go away, others slowly develop into cancer.
Bowel cancer is the fourth most common cancer in the UK and more than 16,000 people die from it every year. But it can be successfully treated if spotted early: most people diagnosed at the earliest stage survive.
NHS England’s Bowel Cancer Screening Programme (NHS BCSP) offers bowel cancer screening every two years to people aged between 60 and 74. A kit is sent in the post for people to use at home and then return. The test looks for blood in poo (faeces), which can be a sign of polyps or bowel cancer. People who receive an abnormal result are invited for a further test (colonoscopy) in which a tiny camera is passed inside the bottom (rectum) to examine bowel tissue for signs of cancer.
The current test for blood in faeces is the FIT (faecal immunochemical test). This replaced the previous test, the guaiac faecal occult blood test (gFOBT) following a successful initial (pilot) study in 2014 comparing the two.
The gFOBT test gave two results: negative or positive. FIT is more informative and gives the amount of blood in faeces. But FIT screening is routinely used in the same way as gFOBT, with a single cut-off threshold (of 120μg/g).
The current screening programme with FIT therefore has only two screening pathways:
- people with results above the threshold are referred for further investigation (usually a colonoscopy)
- people with results below the threshold are offered another FIT test two years later.
The researchers wanted to see if FIT results could be used more fully to improve screening. They wanted to estimate how many cancers were being missed among people with results below the threshold. And they wanted to examine whether looking at graded results – not just a single threshold – could be used to introduce new screening pathways.
The researchers used data gathered as part of the 2014 pilot study which included 27,238 people. Of these, 1,825 had a FIT result of 20μg/g or higher, and they had colonoscopy to detect bowel cancer and polyps.
The research team used this data to develop a model to show how different FIT results relate to the risk of cancer or polyps in the bowel.
The model suggests that the current bowel cancer screening programme may miss a high proportion of cancers and high-risk polyps. It found that the current threshold of 120μg/g:
- is likely to miss more than half of bowel cancer cases (51%)
- identifies one in four high-risk polyps (25%).
A much lower threshold of 20μg/g could identify more (82%) of bowel cancers and high risk polyps (64%) but would mean that many more of those screened (7.8%) would be referred for colonoscopy. This is not practical because of the limited number of specialists to carry out the procedure.
The researchers suggest instead that new screening pathways could be introduced. Different FIT results would determine the screening interval and/or the investigations used.
Why is this important?
These findings highlight the need to improve the national screening programme for bowel cancer. Using a low FIT threshold in the NHS screening programme would demand far more colonoscopies than is currently realistic.
The researchers therefore suggest that the screening programme could make use of FIT results to develop multi-threshold screening pathways. The programme could make use of less invasive or more widely available diagnostic tools such as flexible sigmoidoscopy (only the lower part of the bowel is examined) and capsule colonoscopy (people swallow a tiny camera which passes into the bowel). Methods like these could help identify high-risk individuals without overloading the colonoscopy service.
In a multi-threshold approach, different concentrations of blood found in faeces would trigger different actions. An example of the screening pathways could be:
- blood is undetectable - next screen is delayed to three years
- very low blood concentration - next screen at standard interval of two years
- low blood concentration - screening is repeated at three months
- medium blood concentration - flexible sigmoidoscopy, removal of polyps plus a further FIT to ascertain whether the cause of the bleeding has been removed
- high blood concentration - standard colonoscopy.
The thresholds for each pathway will need to be established before new screening pathways could be introduced.
This research highlights an opportunity to improve the detection of bowel cancer and high-risk abnormalities currently identified by the NHS bowel cancer screening programme in England.
The researchers have suggested that FIT results could be used more fully as part of a programme with multiple screening pathways. But further research is needed to work out the safety and effectiveness of this proposal, and to establish specific thresholds for each pathway.
This study did not take into account detailed information about polyps, such as where they were found in the bowel. Future work should examine this because it influences the amount of blood found in faeces and is associated with the risk of developing bowel cancer.
You may be interested to read
The full paper: Li S J, and others. Faecal Immunochemical Testing in Bowel Cancer Screening: Estimating Outcomes for Different Diagnostic Policies. Journal of Medical Screening 2020;28:3
Related research about faecal testing: Toes-Zoutendijk E, and others. Incidence of interval colorectal cancer after negative results from first-round fecal immunochemical screening tests, by cutoff value and participant sex and age. Clinical Gastroenterology and Hepatology 2020;18:7
Related research about faecal testing: Niedermaier T, and others. Diagnostic performance of flexible sigmoidoscopy combined with fecal immunochemical test in colorectal cancer screening: Meta-analysis and modeling. European Journal of Epidemiology 2017;32
Bowel Cancer UK; the UK's leading bowel cancer charity.
Funding: NIHR Research Methods Fellowship 2017 and the NIHR Policy Research Programme, conducted through the Policy Research Unit in Cancer Awareness, Screening and Early Diagnosis.
Conflicts of Interest: The study authors declare no conflicts of interest.
Disclaimer: NIHR Alerts are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that views expressed in NIHR Alerts are those of the author(s) and reviewer(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.