Polyps Patient Information Fact Sheet

What is a polyp?
A polyp is a fleshy growth on the inside of the bowel. Some people may develop just a single polyp, while others can have two or more at a time. Polyps can either be on a stalk (in which case the polyp resembles a mushroom growing up from the lining of the bowel) or they can be much flatter and even have a broad base. Polyps are benign but they are important because some of them may eventually become malignant (cancerous). Most doctors think that all bowel cancers develop from polyps.

Where do polyps occur in the bowel?
Polyps occur in the lowest part of the intestine, called the large bowel (which consists of all of the colon and the rectum). Polyps seem to be most common toward the lower part of the colon and also in the rectum.

How common are polyps?
Polyps are very common, especially for those of us who live in the western world. About one in four people will have a polyp at some time in their life. Polyps tend to be slightly more common in men than women. They are rather unusual below the age of 40 and occur most often in people over 60. Up to 10% of people who form polyps have others in their family who also have had polyps.

What sorts of polyps are there?
Most polyps are small. They are usually less than one centimeter in size but can grow up to several centimeters. Usually the bowel only contains a single polyp but sometimes there can be more, although it is unusual to have more than five. Apart from coming in different shapes and sizes, polyps also vary in their appearances when looked at under a microscope. Some types of polyps have no potential whatsoever to become cancers. The polyp that it is most important to detect and treat is called an adenoma.

Why do polyps appear?
The lining of the bowel constantly renews itself throughout our lives. There are many millions of tiny cells in the lining that grow, serve their purpose, and then new cells take their place. Each of these millions of cells contains genes that give instructions to the cell on how to behave. When genes behave in a faulty manner, this can cause the cells to grow more quickly, eventually producing a small bump on the bowel surface, which we call a polyp.

Why do polyps get bigger?
A polyp, or more strictly speaking, the particular type of polyp called an adenoma, starts out as a tiny bump on the surface of the bowel. Some polyps remain very small throughout their lives while others continue to enlarge. Most polyps remain benign throughout life but about one in 10 will turn into cancer. Experts believe that all malignancies of the bowel begin as benign polyps; so removing benign polyps can prevent the development of cancer.

Do polyps cause symptoms?
Polyps usually do not cause symptoms, and most people will never know if they have them. Occasionally they can cause bleeding from the rectum. Sometimes polyps produce an excess of mucus, which can be noticed in the stool after a bowel movement. 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.

What tests confirm the presence of polyps?
Polyps can be detected either by colonoscopy or by a barium enema x-ray. Both methods require the bowel to be as clear as possible before the procedure so you will be asked to follow a special diet as well as take laxatives. Both techniques also involve a small tube being passed through the rectum. In the case of a barium enema this is to allow a liquid to be passed into the bowel that will show up on x-rays. In a colonoscopy, a soft flexible tube is passed along the rectum and then through the whole colon. Sometimes a shorter instrument called a sigmoidoscope is used but this can only pass up through the lower colon. If the barium enema does reveal a polyp, a colonoscopy will then be needed to remove it.

The most common reason to carry out an examination of the bowel is that a patient has noticed symptoms, particularly rectal bleeding. Increasingly, patients are being asked to give a sample of their stool for a chemical test that can detect small quantities of blood that are not visible. This test is called “fecal occult blood” test and is likely to be much more widely used as an early screening tool. The idea is that unsuspected polyps might bleed a little, but enough for it to be picked up on a chemical test. Doctors recognize that many bowel cancers can be treated very early or can be prevented by screening.

How are polyps treated?
There are a variety of different techniques to remove polyps but most consist of passing a wire through the colonoscope and looping the wire around the polyp (like a lasso) to remove it. This procedure is quite painless and only one examination is needed to clear the bowel of polyps. Occasionally, there may be too many polyps for all of them to be removed safely at one time and the procedure may need to be repeated.

Once they have been removed, all polyps are sent to the laboratory for microscopic analysis. This will show whether or not the polyp has been completely removed, whether it has the potential to develop malignancy and, of course, to be sure that cancer has not already developed.

Will I need any further examinations?
You will probably need to have a follow-up examination if the microscopic 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 that time, your doctor may either suggest that nothing further need be done or that you should return for a further test in three to five years time.

Further Information
National Cancer Institute: www.cancer.gov
American Gastroenterological Association: www.gastro.org

Last Reviewed: May 2013