Familial adenomatous polyposis (called “FAP”) is a disease that causes abnormal growths in the large intestine (also called the colon), rectum and other areas. Doctors call these growths “polyps.” They are not cancer, but can turn into cancer.
Most people with FAP have hundreds or thousands of polyps. This means they have a much higher risk of colon cancer than other people. Without treatment, almost all people who have FAP will develop colon cancer. Some people have a milder form of FAP that causes fewer polyps.
FAP is caused by an abnormal gene that runs in families. People who have FAP usually start showing signs of it in their teens or 20s, but some people get it in childhood. The average age at which an individual develops colon cancer in classic FAP is 39 years. Some people have a variant of the disorder, called attenuated familial adenomatous polyposis, in which polyp growth is delayed. The average age of colorectal cancer onset for attenuated familial adenomatous polyposis is 55 years.