Colon cancer is an oncological disease. A tumor appears in one of the segments of the organ. Depending on the location of the tumor, it can be cancer of the small or large intestine, including the rectum. Duodenal cancer develops in the initial part of the small intestine. It is rare as an independent disease. More often, it is a secondary neoplasm. Colorectal cancer is a malignant tumor that can occur in the colon and rectum.