Cancer Institute A national cancer institute
designated cancer center

What is Familial Adenomatous Polyposis

Patients with familial adenomatous polyposis can develop hundreds of polyps in the colon and rectum at a young age. On average, polyps appear by age 16, and if the colon is not surgically removed, cancer will occur on average by age 39. The polyps eventually become so dense that they appear as a carpet of polyps upon visualization by colonoscopy or sigmoidoscopy.

Characteristics of FAP

In its classic form, FAP is characterized by the following:

Genetic Mutation Causes FAP

FAP is caused by a mutated adenomatous polyposis coli (APC) gene. Two-thirds of all cases are inherited from a parent with a mutant APC gene, and the remaining one-third of cases arise from a spontaneous APC gene mutation. FAP is a relatively rare syndrome, afflicting about one in 10,000 people. Nearly everyone who has a mutation in the APC gene that causes the classic form of FAP will develop colorectal polyps by age 50, unless they take preventive action. However, the age of onset varies. Consider the following:

Age of Onset
People who have a mutant APC gene who will have polyps in the colon

10 years

15 percent

20 years

75 percent

30 years

90 percent

40 to 50 years

Virtually all people with a mutation who have not had any intervention (such as surgery)


Stanford Medicine Resources:

Footer Links: