In the children of parents who have undergone surgery for colorectal cancer, an initial screening colonoscopy should be performed between ages 35 and 40, depending on the age that your relative was diagnosed. If the screening colonoscopy is normal, the test can be repeated at three to five year intervals. Ask your physician how often colonoscopies should be performed. It is important to remember that a colonoscopy can visualize the entire length of the colon, and polyps that are identified must be removed. On page 10 we referred to the polyp to cancer sequence.
Researchers now have confirmation that cancer arises from polyps over a period of five to ten years.
Removal of all polyps, therefore, can potentially prevent some colon cancers. When cancer is confined to a polyp, it can be completely removed. If it is not found beyond the mucosa or first layer of lining in the colon, it is called in situ , meaning confined to the specific site. The polyp to cancer sequence accounts for some, but not all, colon cancers. Others are thought to arise de novo , that is, beginning as established cancers in the lining of the colon or the colonic epithelium.