Cancer is a class of diseases characterized by out-of-control cell growth. Colon cancer forms when this uncontrolled cell growth happens in the cells of the large intestine.

Most colon cancers originate from small, noncancerous (benign) tumors called adenomatous polyps that form on the inner walls of the large intestine.
Colon cancer cells will invade and damage healthy tissue that is near the tumor, causing many complications.