What is colorectal cancer?

Colorectal cancer is a type of cancer that involves uncontrolled growth of abnormal cells in the colon or rectum. The colon and rectum make up the last sections of the gastrointestinal system.

Colorectal cancer starts in the inner lining of the colon or rectum, usually as abnormal growths called polyps. Polyps may remain benign, but some are precancerous and over the years turn malignant. The polyps most likely to turn cancerous are adenomatous polyps, or adenomas. The adenomatous cells are gland cells on the inner lining of the colorectal tract.

Colorectal cancer can spread from the innermost mucosal layer to the wall of the colorectal tract and beyond. Cancer in the colorectal wall can grow into the blood vessels or lymph vessels. These vessels can allow the cancer to spread to distant parts of the body.

How dangerous is colorectal cancer?

Colorectal cancer is the second deadliest form of cancer in the United States. However, the mortality rate has been dropping for the past 15 years, which is most likely due to improved screening and treatment methods.

The outlook is best when cancer is confined to the innermost layer and does not block or perforate the large intestine. This occurs in the early stages of the cancer. Ninety percent of people treated for early-stage colorectal cancer, before it begins to spread, survive at least five years and often much longer, according to the American Cancer Society.