Cancer, colon: A malignancy that arises from the inner lining of the colon. Most, if not all, of these cancers develop from colonic polyps. Removal of these precancerous polyps can prevent colon cancer.

Colon polyps and early colon cancers cause no signs or symptoms. Full-blown colon cancer can cause occult (a microscopic amount of) blood in the stool, overt rectal bleeding, bowel obstruction, and weight loss.

Risk factors for colon cancer include a family history of it or of colonic polyps, and long standing ulcerative colitis. The overall risk can be reduced by following a diet low in fat and high in fiber.

Colon cancer is preventable and curable. It is preventable by removing the precancerous colon polyps. It is curable if detected early when it can be surgically removed before it has spread to other parts of the body. If screening and surveillance programs were practiced universally, there would be a tremendous reduction in the incidence and mortality of colon cancer.