Hereditary colorectal cancer syndromes characterised by the development of hundreds to thousands of colorectal adenomas. The attenuated form leads to the formation of fewer than 100 polyps.
Caused by germline mutations of the adenomatous polyposis coli (APC) gene.
Colorectal cancer arises in close to 100% of patients with familial adenomatous polyposis (FAP) by 40 years of age and in 80% of attenuated FAP patients by 60 years of age in the absence of either total colectomy or endoscopic polyp clearance.
Prophylactic proctocolectomy is the main means for preventing colorectal cancer in FAP.
Duodenal and periampullary polyps lead to an increased risk for duodenal cancer, which is the most common cause of cancer death in FAP/attenuated FAP patients who have had prophylactic colectomy.
Familial adenomatous polyposis (FAP) syndrome is an autosomal-dominant condition caused by germline adenomatous polyposis coli (APC) gene mutations. Patients with classical FAP have hundreds to thousands of colorectal adenomas and a nearly 100% risk for colorectal cancer by age 40 years if prophylactic colectomy is not performed. Attenuated FAP is also caused by APC mutations and is characterised by fewer than 100 adenomas and a later age of colorectal cancer onset.
FAP features that occur outside the gastrointestinal tract include skin cysts, lipomas and fibromas, supernumerary teeth, thyroid nodules and cancer, osteomas, desmoid tumours, adrenal adenomas, and congenital hypertrophy of the retinal pigment epithelium. Previously, patients with FAP and extra-intestinal features were diagnosed with Gardner's syndrome and patients with FAP and medulloblastomas were said to have Turcot's syndrome. Rare FAP patients with medulloblastomas are said to have Turcot's syndrome. Use of the terms Gardner's syndrome and Turcot's syndrome are historical and should be avoided as they are FAP spectrum phenotypes and are part of APC-associated polyposis. Patients may also find these terms confusing.
History and exam
Key diagnostic factors
- family history of FAP/attenuated FAP
- onset of colorectal cancer in middle age
- bilateral pigmentation of the retina
Other diagnostic factors
- extraintestinal features of FAP
- germline APC gene mutation
- family history of FAP or attenuated FAP
1st investigations to order
- extended-side-viewing oesophagogastroduodenoscopy (EGD)
Investigations to consider
- genetic testing
- abdominal imaging with CT or MRI
FAP: surgery acceptable to patient
FAP: patient averse to immediate surgery with no contraindications to delayed surgery
- MutYH polyposis
- Juvenile polyposis
- Peutz-Jeghers syndrome
- Informed consent for GI endoscopic procedures
- Suspected cancer: recognition and referral
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