A colonoscopy is the standard screening method for bowel cancer. It is generally offered to people who have symptoms of bowel cancer or other bowel-related conditions, and it is not used for mass screening. It might also be offered if you have suffered from cancer in the past or have a strong family history of the disease. A colonoscope is a flexible tube with a light and camera on the end that is inserted into the anus and is moved along the bowel to look for any abnormalities.
The medical professionals will then be able to see the pictures taken inside of your body on a screen. If they see anything concerning, it’s possible to take biopsies and remove growths like polyps during the procedure. Some patients choose to be sedated during the process. It’s a quick procedure, and most people will return home the same day.
Bowel cancer is a type of cancer located in any area of the large bowel (large intestine), which is made up of the rectum and colon. Often, the term ‘bowel cancer’ is used interchangeably with other terms such as ‘colon cancer’, ‘rectal cancer’ or ‘colorectal cancer’. Small bowel (small intestine) cancer also occurs but is less common.
Bowel cancer is one of the most common cancers occurring in the UK.
Screening for colorectal cancer is available in the UK to all between the ages 60 and 74; this age bracket is gradually being lowered to allow younger people to also undergo routine screening. Often, the first sign of colorectal cancer is blood in the stool, but it might not always be visible, so some screening methods that can detect blood and other changes that might indicate cancer or other benign conditions are also being made available.
Any change in bowel habits should be reported to a doctor as soon as you notice them, no matter what age you are. As with all cancers, the earlier they are detected, the easier they are to treat.
Potential drawbacks of colonoscopy:1
- Pain: some patients experience pain during and after the procedure but for most, it is just uncomfortable.
- Bleeding: if polyps are removed, or samples of tissue are taken, you might experience some bleeding. It’s usually nothing serious and will clear up by itself
- Bowel perforation: this is rare, but sometimes the bowel can tear during the procedure
- Adverse reactions to sedation may occur occasionally
Sometimes, a colonoscopy cannot provide a full picture of the bowel, so a CT scan might be needed. Furthermore, colonoscopy isn’t suitable for some patients, so other available colorectal cancer screening tools are used. These will be discussed below.
Faecal immunochemical test (FIT)
How FIT works:
The faecal immunochemical test (FIT) can detect minute traces of blood in a stool sample.2 Blood in the faeces is a symptom of colon cancer but cannot always be seen by the naked eye.
This test is a completely painless process; the patient just needs to provide a stool sample using a kit. The test is used for both people who have symptoms of bowel cancer and also as a screening tool for those who do not have symptoms.
For those who do not have symptoms, the NHS in the U.K. provides free screening to everyone aged 60-74. The age bracket is being gradually lowered over the next four years to make the screening available to all aged 50+.
Test results are usually received within two weeks. If blood is detected in the stool, patients will need further tests. If no blood is detected during routine screening, no further tests are usually carried out unless the patient is experiencing symptoms that could be indicative of colorectal cancer.
- The test can be carried out in the privacy and comfort of the patient's own home.
- The sensitivity to blood in the FIT test can be adjusted depending on whether a patient has symptoms or not.
- Low uptake- only 30% of those offered the screening in England chose to complete the test
- No screening test is 100% reliable
Effectiveness of FIT:
For most people, if the results of the test are FIT-negative (no blood in stool), this means that they don’t have cancer. However, the test is not 100% reliable; some people have a negative FIT test but do have cancer.
A systematic review and meta-analysis state that FIT tests are moderately sensitive and have high diagnostic accuracy when detecting colon cancer.
Stool DNA test (sDNA)
How sDNA works:
A stool DNA test (sDNA) is another method used to detect colon cancer.3,5 Like the FIT test, it can detect blood in the stool but also looks for changes in the cell’s DNA that might indicate a mutation.
If cancer is present in the colon, it sheds cancerous cells into the stool containing changes in DNA that can be picked up by sDNA test. It’s only used as a screening tool and not for those with symptoms.6
- sDNA test can also detect polyps that might be present in the bowels. Polyps can sometimes become cancerous. Most people who have polyps are not aware of its presence until they undergo tests.
- The sample can be provided in the comfort of the patient’s own home and simply put in the post or returned to the doctor’s surgery
- sDNA test is completely painless
- Although the test is effective at detecting DNA changes, further tests such as a colonoscopy will be required if the screening detects polyps or anything abnormal
Effectiveness of sDNA test
In the UK, the FIT test is the standard screening tool for those without symptoms and so there isn’t much data available on the effectiveness of the sDNA test. However, during a small study of Alaskan people, the sDNA test was seen to be more cost-effective than colonoscopy and FIT testing.4
Virtual colonoscopy (VC)
How VC works?
Virtual colonoscopy (VC) is sometimes called computerised tomography (CT) colonography. A CT scan uses X-rays that allow medical professionals to visualise what your bowel looks like from the inside.7 It can be recommended instead of a colonoscopy or might be required after a colonoscopy. Those with a strong family history of bowel cancer might also be offered a VC if other tests, such as the FIT, detected blood in their stool. The test is suitable for those with or without symptoms of cancer.
Before the scan, air and carbon dioxide are pumped through a tube inserted into the rectum to expand the bowel. An injection might also be given to relax the bowel, and some patients receive an injection of contrast dye. These will allow your bowels to be seen more clearly on the scan. Immediately after the test, you might experience bloating and feel uncomfortable. This should only last an hour or so.
Additionally, the bowel must be empty before the scan. Laxatives will be prescribed for you to take at home before the procedure. They are similar to colonoscopy and are called bowel preparation. Patients will also have to follow a special diet in the days before their virtual colonoscopy.
- VC is painless
- Most patients will not need sedation and so will be able to leave the hospital quickly after the procedure.
- There’s no risk of bleeding or perforation from the CT scan itself
- The administration of gas and air into the bowel to expand it can be uncomfortable for some patients and in rare cases, can cause a perforation of the lining of the large intestine.
- Samples of tissue cannot be taken during the scan
- CT scans are expensive.
- Anybody receiving a CT scan is exposed to a small amount of radiation
- Not available in all hospitals
- Some patients find the bowel prep challenging to deal with
Effectiveness of VC:
Although VC can detect changes, such as the presence of tumours and polyps in the bowels, it is unable to detect inflammation or changes in the bowel lining. Unlike a colonoscopy, samples of tissues cannot be taken, and polyps cannot be removed during the procedure. About 94% of polyps that are at least 8mm in size and 88% of polyps less than 6mm in size can be detected.
Capsule endoscopy (CE)
How CE work?
Colon capsule endoscopy involves a small camera, around the size of a large pill, being swallowed.,6 As the camera passes through the digestive system, it takes a large number of pictures that are sent to a device that you wear on your shoulder in a small bag to be later viewed by a medical professional. The capsule then passes naturally during a bowel movement within a couple of days and can be flushed away. CE is used to investigate different conditions, including:
- Unexplained gastrointestinal bleeding
- Crohn's disease and other inflammatory bowel diseases
- Coeliac disease
It can also be used to follow up after other procedures and imaging tests if the results from these are inconclusive.
- The capsule can access your small intestine, which some other tests are unable to do
- The capsule is not difficult to swallow.
- The procedure is painless, and you will be able to resume normal activity whilst the camera is working.
- The procedure is not currently available in all areas
- If anything suspicious is spotted, you will likely need a colonoscopy to look at it further
- The capsule cannot take samples of tissue
- In rare cases, the capsule does not leave the body in a bowel movement and can become lodged in the digestive tract. An X-ray is usually carried out if the patient is not sure if the capsule has passed naturally. An endoscopy or colonoscopy might be necessary to remove the capsule in the unlikely event that the capsule gets stuck.
Flexible sigmoidoscopy (FS)
How FS work?
Flexible sigmoidoscopy is similar to colonoscopy, it involves a scope being inserted through the anus to look inside the body.8 However, FS only looks at the rectum and lower part of the bowel, whereas colonoscopy looks at the bowel in its entirety. FS is sometimes referred to as bowel scope. At one end of the scope, there is a light and camera to allow the medical professionals to view the images on the screen whilst the scope is being moved around.
The bowel must be empty before the procedure, so bowel preparation will be prescribed. Depending on the individual, some medications will also need to be stopped before FS is carried out. You will be informed of this before your procedure.
- FS is quick and painless for most patients
- Samples of tissue can be taken during the procedure, and polyps can be removed.
- The test is usually completed within 15 minutes, and the patient can go home on the same day.
- A small amount of gas is administered into the bowel; this can cause bloating and pain after the procedure.
- Following FS, you might experience a small amount of bleeding, especially if biopsies have been taken or polyps removed.
- There is a very small risk that the bowel might tear, and this would need to be surgically repaired.
To summarise, bowel cancer is very prevalent in the UK, and early detection is essential to attain the best chance of survival. A colonoscopy is the best way to look inside the bowel and detect any abnormalities, but it isn’t used to screen patients routinely. The availability of screening tools such as FIT and sDNA means that, hopefully, bowel cancer can be diagnosed earlier in those who do not have symptoms. There are other tests available for bowel cancer, but they usually require a follow-up with a colonoscopy, and there are benefits and drawbacks for each.
- Kim SY, Kim HS, Park HJ. Adverse events related to colonoscopy: Global trends and future challenges. World J Gastroenterol [Internet]. 2019 Jan 14 [cited 2023 Nov 7];25(2):190–204. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6337013/
- Lee JK, Liles EG, Bent S, Levin TR, Corley DA. Accuracy of faecal immunochemical tests for colorectal cancer: systematic review and meta-analysis. Ann Intern Med [Internet]. 2014 Feb 4 [cited 2023 May 4];160(3):171–81. Available from: http://annals.org/article.aspx?doi=10.7326/M13-1484
- Carethers JM. Faecal DNA testing for colorectal cancer screening. Annu Rev Med [Internet]. 2020 Jan 27 [cited 2023 May 4];71(1):59–69. Available from: https://www.annualreviews.org/doi/10.1146/annurev-med-103018-123125
- Redwood DG, Dinh TA, Kisiel JB, Borah BJ, Moriarty JP, Provost EM, et al. Cost-effectiveness of multitarget stool DNA testing vs colonoscopy or fecal immunochemical testing for colorectal cancer screening in alaska native people. Mayo Clinic Proceedings [Internet]. 2021 May 1 [cited 2023 May 4];96(5):1203–17. Available from: https://www.sciencedirect.com/science/article/pii/S0025619620309319
- Stürzlinger H, Conrads-Frank A, Eisenmann A, Invansits S, Jahn B, Janzic A, et al. Stool DNA testing for early detection of colorectal cancer: systematic review using the HTA Core Model® for Rapid Relative Effectiveness Assessment. Ger Med Sci [Internet]. 2023 Jun 23 [cited 2023 Nov 7];21:Doc06. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10326527/
- Ismail MS, Semenov S, Sihag S, Manoharan T, Douglas AR, Reill P, et al. Colon capsule endoscopy is a viable alternative to colonoscopy for the investigation of intermediate- and low-risk patients with gastrointestinal symptoms: results of a pilot study. Endosc Int Open [Internet]. 2021 Jun [cited 2023 Nov 7];9(6):E965–70. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8159609/
- Ganeshan D, Elsayes KM, Vining D. Virtual colonoscopy: Utility, impact and overview. World J Radiol [Internet]. 2013 Mar 28 [cited 2023 Nov 7];5(3):61–7. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3650206/
- Ko CW, Doria-Rose VP, Barrett MJ, Kamineni A, Enewold L, Weiss NS. Screening flexible sigmoidoscopy versus colonoscopy for reduction of colorectal cancer mortality. International journal of colorectal disease [Internet]. 2019 Jul [cited 2023 Nov 7];34(7):1273. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7071949/