Introduction

Colorectal cancer is a well-known and commonly diagnosed condition that affects both men and women, usually at age 50 or above. Cancer of the colon or rectum will be the third most commonly diagnosed type of cancer for both men and women in the United States in 2008. 

Colorectal cancer starts either in the colon or rectum. Because cancer of the colon (colon cancer) and cancer of the rectum (rectal cancer) have many common features they are often simply called "colorectal cancer." Other names for this condition are cancer of the large intestine and cancer of the large bowel.

The colon and rectum are part of the large intestine—a long, thick, winding tube that performs the final steps in digesting food. The colon forms most of the large intestine. It soaks up water and minerals from food, converts food to waste, and allows it to exit the body. The rectum is the last segment of the large intestine. It holds solid waste until it leaves the body through the anus as part of a bowel movement.

Although the exact causes of most colorectal cancers are unknown, certain risk factors have been identified. These include older age, ulcerative colitis (a disease causing inflammation of the colon), and a previous or family history of colorectal cancer. Most colorectal tumors begin as noncancerous (benign) polyps on the wall of the colon or rectum.