Colorectal Cancer Overview

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The colon and rectum are part of the digestive tract. Together, they comprise the large intestine, or large bowel, which is located in the abdomen between the small intestine and the anus. Cancer that originates in the colon or rectum may be called colon cancer, rectal cancer, or colorectal cancer. Colon cancer is the term most commonly used to refer to this type of cancer.

The colon is primarily responsible for absorbing water. It is about 6 feet in length and consists of the cecum (connects to the small intestine at the ileocecal valve), the ascending colon (the vertical segment located on the right side of the abdomen), the transverse colon (extends across the abdomen), the descending colon (leads vertically down the left side of the abdomen), and the sigmoid colon (extends to the rectum).

The rectum is the last segment of the large intestine. It is 8 to 10 inches in length and leads to the anus, which is the opening to the outside of the body. Waste material (fecal matter) is stored in the rectum until it is eliminated from the body through the anus.

Most (over 95%) colon cancers are adenocarcinomas that develop when a change (i.e., mutation) occurs in cells that line the wall of the colon or rectum. The disease often begins as an intestinal polyp, also called an adenoma, which is an abnormal growth of tissue. Polyps gradually can become precancerous and then cancerous.