Familial adenomatous polyposis, or FAP, is a genetic disorder characterized by extensive polyps in the digestive tract and colorectal cancer. Dr. Malone, can you tell us more about FAP?
Of course, Major Spencer. FAP is caused by mutations in a specific gene known as the APC gene. These mutations affect the ability of the cell to maintain normal growth and function, so the tissues continue to grow even when they aren't supposed to. Cell overgrowth resulting from mutation, therefore, leads to colon polyps. There is also a modified version of FAP, called MUTYH, in which only part of the APC gene is mutated.
People with FAP may begin to develop numerous polyps in the colon as early as their teenage years. As they age, the number of polyps increases, and eventually hundreds of thousands of polyps can develop. MUTYH tends to result in fewer polyps than FAP -- anywhere from 10 to 100 polyps instead of hundreds of thousands -- as well as development of polyps at a slightly later age.
Unless the colon is removed, these polyps will become malignant, or cancerous. The average age at which a person with FAP develops colon cancer is 39 years.
People with FAP also have benign, or noncancerous, growths called desmoid tumors. These tumors usually occur in the tissue covering the intestines and tend to recur after they've been surgically removed.
In some cases, both benign and cancerous tumors are found in other parts of the body as well, some in the digestive tract, such as the stomach and small intestine, and some in other areas of the body, such as the bones, skin, and other tissues.