The colon and rectum are part of the large intestine (large bowel). Colon and rectum cancers, which are sometimes referred to together as "colorectal cancer," arise from the lining of the large intestine. (When cancer arises from the lining of an organ like the large intestine, it is called a carcinoma.)

There are over 130,000 cases of colorectal cancer diagnosed in the United States each year, and over 50,000 deaths. Colorectal cancer is the second leading cause of cancer deaths. In almost all cases, however, this disease is entirely treatable if caught early by colonoscopy.

There is no single cause for colon cancer. However, almost all colon cancers begin as benign polyps which, over a period of many years, develop into cancers.

Factors that increase the risk of colon cancer are colorectal polyps, cancer elsewhere in the body, a family history of colon cancer, and ulcerative colitis.

Patients with a history of breast cancer have a slightly increased risk of developing colon cancer. Certain genetic syndromes increase the risk of developing colon cancer in affected families.

Dietary factors that have been associated with colon cancer are a high-meat, high-fat, low-fiber diet. However, some studies found that the risk is not reduced when people switch to a high-fiber diet, so the cause of the link is not yet clear.