Colonic polyps are fleshy growths that occur on the inside of the large intestine, also known as the colon. Polyps in the colon are extremely common, and their occurrence increases as individuals grow older. It is estimated that 50% of the people over the age of 60 will have at least one polyp. The significance of polyps is that when certain types of polyps grow large enough, they can become cancerous. Colon cancer is a cancer from uncontrolled cell growth in the colon; it is the third most commonly diagnosed cancer in the world, but it is more common in developed countries: approximately 60% of cases were diagnosed in the developed world. Colon cancer is the second leading cause of death from cancer in the United States. It is estimated that there were 143,460 new cases of colorectal cancer in the United States in 2012, with 51,690 deaths.
The risk of a colon polyp becoming cancerous increases as the size of the polyp increases. Therefore, screening for colon polyps and removing them before they become cancerous should markedly reduce the incidence of colon cancer. Many doctors in the U.S. are recommending colonoscopies to screen healthy subjects with an average risk of developing colon cancer. Colonoscopies are recommended beginning at the age of 50 and every 7–10 years thereafter if no colon polyps or cancers are found. Unfortunately, many patients do not undergo screening due to the perceived inconvenience and discomfort of existing screening tests. CT colonography (CTC), a CT-scanbased imaging method, has been under study for the past ten years and shows promise as a method of colorectal cancer screening that may be acceptable to many patients. Figure 1.1 shows the colon anatomy and a colonic polyp shown in the optical colonoscopy and CTC.
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