Colorectal (large bowel) cancer is a disease in which malignant (cancer) cells form in the inner lining of the colon or rectum. Together, the colon and rectum make up the large bowel or large intestine. The large intestine is the last segment of the digestive system (the esophagus, stomach, and small intestine are the first three sections). The large bowel’s main job is to reabsorb water from the contents of the intestine so that solid waste can be expelled into the toilet. The first several feet of the large intestine is the colon and the last 6 inches is the rectum.
Most colon and rectal cancers originate from benign wart-like growths on the inner lining of the colon or rectum called polyps. Not all polyps have the potential to transform into cancer. Those that do have the potential are called adenomas. It takes more than 10 years in most cases for an adenoma to develop into cancer. This is why some colon cancer prevention tests are effective even if done at 10-year intervals. This 10-year interval is too long, in some cases, such as in persons with ulcerative colitis or Crohn’s colitis, and in persons with a strong family history of colorectal cancer or adenomas.