Familial adenomatous polyposis

What is familial adenomatous polyposis (FAP)?

FAP is an autosomal dominant syndrome characterized by innumerable bowel polyps and other findings. Spontaneous genetic mutations occasionally result in this syndrome.

What is the risk of developing CRC in patients with FAP syndrome? 

FAP syndrome presents as more than 100 adenomas throughout the colon and is caused by mutations in the APC gene.

The risk of developing CRC in patients with FAP is almost 100% by age 40 to 50 years. Total colectomy is indicated in patients with FAP who develop multiple, diffuse adenomas in the colon.

What is the most common location of the polyps in patients with FAP?

Colon > stomach > duodenum > small bowel.

When should endoscopic screening begin in patients with FAP? 

Genetic testing should be offered to all patients at risk for FAP and to family members prior to endoscopic screening. Beginning at age 10 to 12, individuals at risk for FAP should undergo annual flexible sigmoidoscopy until 40 years of age and then every 3 to 5 years thereafter.

Family members are assumed not to be affected if their genetic test is negative and the index case is positive but can be offered sigmoidoscopy every 7 to 10 years to account for any potential errors in the test.

What are the major variants of FAP?

Attenuated FAP, characterized by <100 adenomatous polyps in the colon and older age of diagnosis; familial polyposis coli, characterized by multiple enteric polyps; and Gardner’s syndrome, characterized by a combination of enteric polyps, osteomas, soft tissue tumors (e.g., desmoid tumors, ampullary/duodenal tumors, and papillary thyroid cancers), and dental abnormalities.

What is the risk of colorectal cancer among patients with untreated FAP?

Virtually 100% by approximately 35 years of age.

What is the treatment for FAP?

Prophylactic total colectomy at about 20 years of age.

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