What is the recommended screening protocol for Familial Adenomatous Polyposis (FAP)?

Screening Protocol for Familial Adenomatous Polyposis (FAP)

For individuals with FAP or at risk for FAP, flexible sigmoidoscopy should begin at age 10-12 years and continue annually until colectomy is planned. 1, 2, 3

Genetic Testing

• Genetic counseling and APC mutation analysis should be offered to all patients with suspected FAP, as identifying the causative mutation allows for targeted screening of at-risk family members 3
• Full germline genetic testing of APC should include DNA sequencing and large rearrangement analysis 2, 3
• In families where the causative mutation is identified, presymptomatic testing should be offered to first-degree relatives 3
• When no mutation is identified, all at-risk family members should undergo colorectal screening 3

Colorectal Screening Protocols

For Classical FAP:

• Flexible sigmoidoscopy should be performed every 1-2 years starting at age 10-12 years and continued lifelong in mutation carriers 1, 2
• Once adenomas are detected, annual colonoscopy should be performed until colectomy is planned 2, 3
• Surgery is indicated when there are large numbers of adenomas or adenomas showing high-grade dysplasia 2

For Attenuated FAP:

• Total colonoscopy should be performed every 2 years starting at age 18-20 years and continued lifelong in mutation carriers 2
• Colonoscopy is preferred over sigmoidoscopy due to the tendency toward right-sided colonic adenomas in attenuated FAP 1

Screening for Extracolonic Manifestations

• Gastroduodenal endoscopy using both front and side-view scopes should be performed every 5 years until adenomas are detected 2
• Upper GI screening should start when colorectal polyposis is diagnosed or at age 25-30 years, whichever comes first 2, 3
• Annual cervical ultrasonography is recommended for thyroid cancer screening 2, 3
• Regular physical examination and abdominal CT should be performed, especially in patients with a positive family history of desmoids or after abdominal surgery 2

Post-Surgical Surveillance

• After colorectal surgery, surveillance of the rectum or pouch should be carried out regularly 2, 3
• For patients with ileoanal pouch, surveillance should be performed every 6 months to 5 years depending on polyp burden 3

Special Considerations

• Patients with mutations between codons 1250 and 1464, especially codon 1309, have a more severe form of FAP requiring more aggressive surveillance 3, 4
• Patients with codon 1309 mutations develop symptoms and colorectal cancer approximately 10 years earlier than those with other mutations 4
• In approximately 30-40% of FAP cases, there is no family history, suggesting a de novo mutation origin 3
• Attenuated FAP (AAPC) is associated with fewer adenomas (usually 20-100), right-sided colonic adenomas, and later onset of colorectal cancer (approximately 10 years later than classical FAP) 1

Common Pitfalls and Caveats

• Delaying screening beyond age 10-12 in classical FAP can lead to missed early polyp development, especially in patients with severe mutations like codon 1309 3, 4
• Sigmoidoscopy alone is inadequate for screening attenuated FAP due to the predominance of right-sided polyps 1
• Failure to screen for extracolonic manifestations can lead to missed upper GI cancers, thyroid cancers, and desmoid tumors 2, 3
• Without genetic testing, unnecessary invasive screening procedures may be performed on family members who don't carry the mutation 5