For more information, refer to the section of this document on staging. Colon cancer and rectal cancer have many features in common. Sometimes they are referred to together as colorectal cancer . They will be discussed together in this document except for the section about treatment. At that point they will each be discussed separately.
Cancer can develop in any of the four sections of the colon or in the rectum.
Cancer beginning in these different areas may cause different symptoms. Some tests are better at finding cancer on the right side of the colon while others work better at finding cancer on the left side of the colon or in the rectum. Colorectal cancers are thought to develop slowly over a period of several years. Before a true cancer develops, there usually are precancerous changes in the lining of the colon or rectum. These changes might be dysplasia or adenomatous polyps .