Hereditary nonpolyposis colon cancer (HNPCC) is caused by a mutation in any of five genes. Most people have about a six percent chance of developing colon cancer at some point in their lives, usually after age 60. People with HNPCC have about an 80 percent chance of developing colon cancer, usually by age 44. Since they're in a high-risk category, the American Cancer Society recommends that people with HNPCC have their first colonoscopy at age 20, with follow-up colonoscopies every year or two.
A study published in the journal Gut went one step further and asked: Should people with HNPCC also have their small intestine checked out on a regular basis? Long story short, they answered "no" to their own question. Turns out the chance that someone with HNPCC will develop cancer of the small intestine is about one in 25, and the researchers decided the potential benefit didn't outweigh the risk. However, they suggested that people with HNPCC consider having their small intestine examined if they're experience unexplained iron-deficiency anemia or abdominal discomfort.
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Source: Kate, G. and Kleibeuker, J. "Is Surveillance of the Small Bowel Indicated for Lynch Syndrome Families?" Gut (4 Apr. 2007): Published online ahead of print. Accessed 7 April 2007.

