Colon Polyps


Colon polyps are fleshy growths that occur on the inside (the lining) of the large intestine, also known as the colon. Polyps in the colon are extremely common, and their incidence increases as individuals get older. It is estimated that 50% of the people over the age of 60 will harbor at least one polyp. The significance of polyps is that we know that when certain types of polyps grow large enough, they can become cancerous, and, moreover, colon cancer is the second leading cause of death from cancer in the United Sates. Therefore, screening for colon polyps and removing them before they become cancerous should markedly reduce the incidence of colon cancer.

What types of polyps become cancerous?
The polyps that become cancerous are called adenomatous polyps or adenomas. Adenomas account for approximately 75% of all colon polyps. There are several subtypes of adenoma that differ primarily in the way the cells of the polyp are assembled when they are examined under the microscope. Thus, there are tubular, villous, or tubulo-villous adenomas. Villous adenomas are the most likely to become cancerous, and tubular adenomas are the least likely.

What other types of polyps are there in addition to adenomas?
Although adenomas are by far the most common type of colon polyps, there are several other types of polyps. Among the other types of polyps that have no malignant potential are the hyperplastic, inflammatory, and hamartomatous polyps.

What are the guidelines for screening individuals for polyps in order to prevent colon cancer?
Knowing that colon polyps grow and go on to become cancerous and knowing how common they are, screening guidelines have been set by the American Cancer Society to minimize the risk of colon cancer by detecting and removing polyps.

Starting at the age of 40, everyone should have a stool specimen tested for occult blood (blood that cannot be seen with the naked eye) every year. This is recommended because it is known that when polyps become large they can bleed into the intestine where the blood mixes with the stool. Thus, an early warning sign for colon polyps could be the presence of occult blood in the stool.

Starting at the age of 50, everyone should have a flexible sigmoidoscopy every 3-5 years. A flexible sigmoidoscope is a two and one-half foot tube half an inch in diameter with a light on the end that can be inserted through the anus for inspecting the inside of approximately one-third of the colon's total length.

If adenomatous polyps are detected with sigmoidoscopy, then a full colonoscopy with a longer tube (four to five feet) should be used to inspect the entire length of the colon. During a colonoscopy, any polyp can be removed and sent for an evaluation under the microscope to determine if it too is an adenomatous polyp.

Many doctors in the US are recommending screening colonoscopies rather than flexible sigmoidoscopies for healthy subjects with an average risk for developing colon cancer. Colonoscopies are recommended beginning at the age of 50 and thereafter every 7-10 years if no colon polyps or cancers are found. The rationale for this recommendation is: 1) Colonoscopy examines the entire colon while flexible sigmoidoscopy only examines the rectum and the colon adjacent to the rectum, 2) approximately 50% of colon polyps (and colon cancers) are found in the upper colon (cecum, ascending colon, and transverse colon) and, therefore, are beyond the reach of sigmoidoscopes and would be missed by flexible sigmoidoscopy, and 3) the National Polyp Study, a large, scientific study, has shown that colonoscopy with removal of all colon polyps reduces deaths from colon cancer.