Colon and rectum cancer, sometimes called colorectal cancer, begins in the colon or the rectum, which are both parts of the lower digestive system. These cancers are distinct from anal cancer. Most colorectal cancers develop gradually and begin as polyps, or benign tumors, on the inner lining of the colon or rectum. Pre-cancer may also take the form of dysplasia, which is a group of abnormal cells. Cancer that begins in the colon or rectum may become invasive and grow through the wall of the colon or rectum and invade blood or lymph vessels. Most colorectal cancers are adenocarcinomas, which begin in glandular cells.
