Animated Medical Graphics

Colon Cancer

Alimentary tract

The alimentary tract is a tube that extends from the mouth to the anus and consists of different parts with different functions; these parts are as follows: mouth (oral cavity), oropharynx, esophagus, stomach, small intestine (subdivided into duodenum, jejunum, and ileum), large intestine (subdivided into cecum, colon, and rectum) and anus. The large intestine is shown in the picture on the left, starting as the cecum (the pouch with the appendix attached) and extending to the anus. The term colon cancer, or more specifically colorectal cancer, really refers to cancer arising in any part of the large intestine (illustrated on the left).

The exact cause of colon cancer is not known. Although certain other diseases such as familial polyposis and inflammatory bowel disease are associated with it, colon cancer in the vast majority of individuals has no predisposing diseases. Diet has been implicated in the formation of colon cancer since this disease is more common in countries like the U.S. where much of the food consumed has a low fiber content. To learn more about the formation of cancer in general, see Cancer: Genesis.

Colon cancer is usually a type of cancer called carcinoma (or more specifically, adenocarcinoma). It usually starts as cancer although sometimes it may start as a benign (non-cancerous) tumor called an adenoma. It begins in the inner lining (mucosa) of the large intestine as a button-like bump. It grows outward, destroying and replacing normal tissue and frequently disintegrates in its center to form an ulcer. Most of the time the cancer first erodes throught the intestinal wall and grows into the fat that holds the intestine in place and then involves the lymph nodes in the fat. The lymph nodes are pellet-like bits of pink tissue that act as filters. Click here to see this sequence of events animated. The cancer may at times spread to the nodes before penetrating the intestinal wall. If allowed to grow further, the cancer spreads through the bloodstream to the liver. Once it has reached this stage it is extremely difficult to successfullytreat.

As with other cancers, the earlier that colon cancer is detected, the better the chances of survival. A laboratory test used to detect colon cancer early is the occult blood test. This test depends on the fact that colon cancer disintegrates in its center and starts to bleed slightly. If the blood in the stool is not enough to see with the eye, it still may be found by using the chemical (occult) test for blood. However, a positive test for blood in the stool does not automatically mean cancer since there are other causes of blood in the stool.

Note: The material provided in this web page is educational in nature and not medical advice. It is meant neither for self-diagnosis nor as a treatment recommendation. If you are concerned about any condition you think you may have, CONSULT YOUR DOCTOR.