This factsheet is about polyps in the large bowel.
A polyp is a fleshy growth on the inside of the large bowel. Some people may develop just a single polyp, while others can have two or more at a time.
Polyps seem to be very common, especially in the West, and are slightly more common in men than women. They are rather unusual below the age of 40 and seem to occur most often in people over the age of 60.
What does a polyp look like?
A polyp, which is a fleshy growth on the inside of the large bowel, can either be on a stalk (which can look like a mushroom growing from the lining of the bowel) (Fig.1) or it can be much flatter and even have quite a broad base. (Fig. 2)
Polyps are usually benign (not containing cancer) but it’s important they are removed because some of them may eventually become malignant (cancer containing). Most experts now believe that many bowel cancers develop from polyps. Doctors are most concerned about detecting and treating a type of polyp called an adenoma polyp. This is because adenoma polyps are most likely to become cancerous in the future. It is thought that around 1 in 10 adenomatous type polyps will become cancer containing polyps.
What causes the development of polyps in the bowel?
The lining of the bowel, like other organ linings, constantly renews itself throughout our lives. There are many millions of tiny cells in the lining, which grow, serve their purpose and die before new cells then take their place. Each of these millions of cells contains genes, which give instructions to the cell on how to behave and grow. When genes behave in a faulty manner, this can cause the cells to grow quicker, eventually producing a small bump on the bowel surface that we call a polyp.
A polyp, or more strictly the particular type of polyp called an adenoma, starts out as a tiny bump on the surface of the bowel. The genes give faulty instructions that can make the cells grow more quickly but they do so in an orderly manner. Some polyps remain very small (less than one centimetre) while others continue to enlarge up to several centimetres.
Most polyps remain benign (non-cancerous) but it is thought that most malignancies of the bowel begin as benign polyps. So by removing benign polyps we can help to prevent the development of the rare ones that may become cancer.
Can polyps be inherited?
In most cases neither polyps, nor indeed bowel cancer, tend to run in families. However, we do now know that up to 1 in 10 people who have polyps may have them because the likelihood of that happening is inherited (runs in families). When several members of the same family have had polyps or bowel cancer – then there is an increased risk. The increased risk is especially relevant if they have developed polyps or bowel cancer at a young age.
How are polyps in the bowel diagnosed?
Rectal bleeding is a symptom of polyps, both benign and malignant as well as other potentially serious conditions. Investigations will be carried out to determine whether any of these conditions are the cause of the bleeding.
Faecal Immunochemical test (FIT):
These are home testing kits that can pick up hidden blood in poo that is not visible to the naked eye. The results of this test can aid any potential diagnosis or decision about referral to a specialist. This test is not a direct test for polyps, but it can indicate that polyps are more likely to be found in the large bowel, leading to a referral from your doctor for a colonoscopy (see below). We encourage everyone who is eligible to take part in the FIT test screening programme. The test might be off-putting, but it is a small task to perform that has real and potentially life-saving benefits.
This is where a tube, linked to a highly magnified video system is passed via the anus, into the colon. Plus, where possible, the nearest part of the small bowel. A colonoscopy gives a very accurate picture of the lining of the bowel and allows the doctor, or nurse endoscopist, to check for polyps. Sometimes a shorter instrument called a sigmoidoscope is used. The sigmoidoscopy only allows inspection of the lower bowel. If it reveals a polyp, a colonoscopy will still then be needed to remove and to check that there are no more polyps elsewhere in the large bowel. In most cases, sedation is given to minimise any feelings of discomfort or anxiety.
CT Pneumocolon Scans:
This involves air being introduced into the bowel by a small tube, to improve the views of the bowel while the scanning is happening.
Except for the faecal immunochemical test and the faecal occult blood test, all of the above will require the bowel to be as clear as possible before the procedure so that any polyps can be seen. A special diet is followed for a short period, and laxatives are taken at home beforehand. Although this is not pleasant, the laxatives are taken in the right amount needed to clear the bowel and it is advisable to stay near a toilet.
We encourage everyone who is eligible to take part in the FIT test screening programme.
In England all men and women aged 60 to 74, who are registered with a GP are automatically sent a bowel screening test every 2 years. In 2021 this will include people aged 56. The age range is planned to be expanded to age 50 over the next 4 years.
In Scotland screening starts at aged 50 to 74.
In Wales the age range is 58 to 74.
In Ireland the age range is 60 to 69
How can polyps in the large bowel affect you?
Usually polyps do not cause symptoms and most people will never know if they have them. However occasionally some people will need investigation and treatment.
Polyps are often discovered at colonoscopy as part of an investigation into bowel changes or symptoms and usually the polyps are not the cause of those symptoms. Occasionally they can cause bleeding from the back passage or may produce an excess of mucus or slime, which can be noticed on motions when opening the bowel. Very occasionally a polyp can grow so large as to cause a blockage of the bowel but, unless this occurs, polyps do not cause pain.
Will polyps in the bowel affect me over time?
Polyps rarely cause day to day problems. However, the main concern is that they may become malignant and cause cancer in the future. You will probably need to have a follow-up examination if the microscope findings indicate the polyp has any malignant potential. If so, your doctor will recommend a repeat colonoscopy in the future to check whether new polyps have grown.
Depending on what is found at the time, your doctor may suggest that nothing further is required or that you should return for a further test in three year’s time.*
If you have a family history of either polyps or bowel cancer, then your doctor may recommend that you have a regular colonoscopy. If you are an individual who tends to form polyps, your bowel should be regularly inspected and any polyps that have formed should be removed. Your doctor may mention the term ‘adenoma’ which is the most common type of polyp that has cancerous potential.
You do not need a special diet and can eat normally. However, a healthy diet, which includes a wide variety of foods and plenty of fruit and vegetables, is good for your general health and to produce good bowel movements. Aim to have regular fruit and vegetables (with meals as well as snacks) and to drink at least two litres (8-10 cups) of fluid every day.
Please see Guts UK’s Healthy Eating & The Digestive System information here.
What treatment is available?
There are a variety of different techniques to remove polyps. Most consist of passing a wire through the colonoscope and looping wire around the polyp – like a lasso – to remove it. This procedure is quite painless and only one examination is usually needed to clear the bowel of polyps. Occasionally, there may be too many polyps for all of them to be removed safely at once and so the procedure may need to be repeated.
Removal of a polyp using a colonoscope and a looping wire:
Once they have been removed, if possible all the polyps are retrieved and sent to the laboratory for microscopic analysis. This will show whether the polyp has been completely removed, where or if it has the potential to develop malignancy and, of course, to be sure that cancer has not already developed.
Polyp removal is quite painless and only one examination is usually needed.
What to ask your doctor?
- What type of polyp do I have, is it benign or malignant?
- How often should I have a follow up colonoscopy?
- Has my family history been noted and taken into account?
- What other follow up do I need?
The British Society of Gastroenterology (the professional body for gastroenterologists) produce guidelines with a summary for people with polyps and their families and carers and it can be found on the British Society of Gastroenterology website.
You can find our more about FIT testing here.
Guts UK are proud to be funding research by Professor Colin Rees, COLO-COHORT (Colorectal Cancer Cohort Study) which aims to identify and build a more detailed screening programme for those who are at increased risk of developing bowel cancer. Bowel cancer, when identified early, is one of the more preventable cancers. This Guts UK-funded research has the capacity to save lives, by developing a robust screening programme for the UK and bowel cancer. Read more here.
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