Cancers of the colon and rectum are the second leading cause of cancer death in the United States. In the past, prevention of colon cancer focused on detecting and removing potentially cancerous polyps (or, projecting growths). More recently, researchers found that colon cancer could also arise from flat, or non-polypoid, lesions in the colon.

In a recent article in the Journal of the American Medical Association, physicians from the Veterans Affairs Palo Alto Health Care System found that non-polypoid colon lesions are diagnosed during routine colonoscopy in approximately 9% of patients. And, these flat lesions were almost ten times more likely to contain cancerous tissue than polyps, regardless of size.

Non-polypoid growths are more difficult to detect by colonoscopy because it may be hard to distinguish them from the normal membrane of the colon, especially if the colon isn't thoroughly emptied at the time of examination. Newer imaging techniques, such as computed tomography (CT) colonoscopy, need to be studied to determine whether they can accurately detect these flat lesions. In particular, depressed non-polypoid lesions seem to be the most difficult to detect, and they also have the highest risk of being cancerous at the time of diagnosis. Although further investigation is needed, this article highlights the importance of both thorough, routine colon cancer screening and a well-trained gastroenterologist.