olon cancer, more accurately called colorectal cancer, includes cancers of the rectum and colon. It usually begins with polyps, small benign growths in the inner wall of the colon or rectum. Some polyps (especially those known as adenomas) become malignant for reasons that are largely unknown. Age is a risk factor: most people who get colon cancer are over 50. Environmental factors—particularly smoking—also play a role. Ulcerative colitis or any other chronic inflammatory bowel disease puts you at higher risk. Family history of colon cancer is a risk factor, too.

But not all the old hunches have proved out. Dietary fiber, for instance, may not play a protective role. And red meat may not be as clear a risk as once was thought.

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