source: Genetic and Rare Diseases (GARD) Information Center
Familial adenomatous polyposis (FAP) is an inherited condition that causes cancer of the large intestine (colon) and rectum. People with the classic type of FAP usually develop hundreds to thousands of noncancerous (benign) polyps (growths) in the colon as early as their teenage years. Overtime, these polyps can become malignant (cancerous), leading to early-onset colorectal cancer at an average age of 39 years. Other signs and symptoms may include dental abnormalities; desmoid tumors; and benign and malignant tumors of the duodenum (a section of the small intestine), stomach, bones, skin, and other tissues. Some people have a milder form of the condition called attenuated familial adenomatous polyposis (AFAP) which is generally characterized by fewer colon polyps (an average of 30) and a delay in the development of colon cancer by 10-15 years. FAP is caused by changes (mutations) in the APC gene and is inherited in an autosomal dominant manner. People with FAP usually undergo regular screening until they develop 20 to 30 polyps and then a colectomy (removal of colon) is generally recommended.
National Institutes of Health