Last updated 2mo ago
A teenager is found to have hundreds of colonic polyps on colonoscopy. His father had colon cancer at age 35 after being diagnosed with FAP. Extracolonic findings include osteomas and dental abnormalities.
AD; APC (adenomatous polyposis coli) - tumor suppressor
- ~30% de novo
- Hundreds to thousands of adenomatous polyps (by teens)
- 100% lifetime risk of colorectal cancer without colectomy
- Extracolonic: Upper GI polyps, desmoid tumors, osteomas, CHRPE, dental abnormalities
- Gardner syndrome: FAP + osteomas + soft tissue tumors
- Turcot syndrome: FAP + CNS tumors (medulloblastoma)
- Clinical diagnosis when more than 100 colorectal adenomas are present (classic FAP); fewer adenomas (10-100) with later onset suggests attenuated FAP
- Confirm with germline APC testing; if APC-negative with an adenoma count of 10-100, test for biallelic MUTYH variants (autosomal recessive MUTYH-associated polyposis is the main differential)
- CHRPE on ophthalmologic exam and supernumerary teeth or osteomas on imaging support the diagnosis in equivocal cases
- Colonoscopy starting age 10-12
- Prophylactic colectomy (typically late teens)
- Upper GI surveillance
- Desmoid surveillance
A Prophylactic Colectomy (APC) if APC is mutated: FAP is caused by APC mutations. APC normally inhibits DNA replication (tumor suppressor on chr 5q21). APC mutation is PanColonic and involves the rectum (vs Lynch, which has no polyps).
"Colorectal cancer runs in the FAMMiLY": FAP = APC, Microsatellite/MMR = Lynch.
Gardner's patients are "Guarded": Gardner syndrome = FAP + osseous (osteomas) and soft tissue tumors, with face/jaw involvement. Turcot = FAP + brain tumors (Turban on the head).