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.