The colon and rectum.

The rectum and the colon are part of a person's digestive system, also called the gastrointestinal tract. Food passes from the stomach into the small intestine and from there, to the colon (or large intestine) and rectum. The small intestine absorbs nutrients while the colon mainly absorbs the water in food, as well as some vitamins. Along with the rectum, the colon also acts as a storage area for solid wastes.

The colon has four sections:

• ascending colon
• transverse colon
• descending colon
• sigmoid colon

Colorectal cancers can occur in any of these four areas of the colon or in the rectum. Almost all colorectal cancers develop from small, mushroom-shaped growths called polyps. Polyps are abnormal growths in the lining of the walls of the colon and rectum. Cancers that develop from these polyps are called adenocarcinomas.

Most polyps are benign (not cancerous), but the risk of a polyp developing into cancer increases over time and with the number and size of the polyps present. For this reason, your doctor will recommend that all benign polyps be removed. Once a polyp has been removed, it can also be checked to ensure that cancerous cells are not present.

Polyps and colorectal cancers are more common in people who live in Western, industrialized societies, like Canada, due to a variety of diet and lifestyle factors. These factors are discussed in the prevention section.

Colorectal cancer is also more common among Hispanics, African-Canadians and Ashkenazi Jews.