Familial adenomatous polyposis
Familial adenomatous polyposis (FAP) is a syndrome inherited as an autosomal dominant trait and characterized by multiple (>100) adenomatous colorectal polyps (adenomas). It is the most common polyposis syndrome known to man or beast. Almost all patients with FAP will develop polyps in adolescence, and 100% of patients will develop colorectal adenocarcinoma (colon cancer) without treatment.
Treatment is a colectomy, usually performed on diagnosis. There are a number of extracolonic and extra-GI manifestations of FAP, the most important of which is the presence of adenomas in the stomach and duodenum, especially around the ampulla of Vater. These adenomas can undergo malignant change.