Colorectal cancer includes cancers of the colon, rectum, appendix, and some anal cancers.
Almost all cases of colorectal cancer begin with the development of benign colorectal polyps. Polyps form when cells lining the colon grow, divide, and reproduce in a disorderly way, producing a growth. If the cells of a polyp acquire the ability to invade into the intestinal wall and thus spread to other parts of the body, a malignant or cancerous tumor develops. Colorectal cancer is the second leading cancer killer, second only to lung cancer. Although colorectal cancer can strike at any age, more than 9 in 10 new cases are in people aged 50 or older.