Familial Adenomatous Polyposis

Background/Epidemiology

  • Autosomal dominant disorder- mutation of the tumour suppressor gene APC (loss of function truncation)
    • NB around 20% have no family history
  • Prevalence of around 1/13000
  • Accounts for ~1% of colorectal cancers
  • Colorectal cancer will develop in 90% of patients before the age of 50.
    • Many patients will have prophylactic colectomy.  However, polyposis is often not confined to the colon and can occur in the duodenum (up to 90% of patients) which can also have malignant potential.

Presentation

  • Patients are often asymptomatic (there may or may not be a family history)
  • If symptomatic, presentation is often that (or similar to that) of colorectal cancer i.e.
    • PR bleeding/mucous discharge
    • Change in bowel habit (diarrhoea>constipation)
    • Abdominal pain
  • Other possible symptoms include
    • Obstructive symptoms e.g. constipation, vomiting, peritonitis
  • Polyps may be palpated on DRE
  • Other signs can include
    • Dental problems
    • Peripheral desmoid tumours
      • (locally invasive fibrous tissue tumours)
    • Osteomas
    • Thyroid masses
    • Congenital hypertrophy of the retinal pigment epithelium

Investigations

  • Sigmoidoscopy/Colonoscopy with biopsy will clinically identify the polyposis
    • Other tests to consider would be
      • Bloods e.g. FBC, LFT (mets), TFTs (if thyroid mass)
        • Carcinoembryonic antigen (cancerous transformation)
      • Imaging
        • CT (? any suspicious masses)
        • Dental, chest and skull x-rays may identify bony lesions
    • Genetic testing can be done to identify the causative mutation and determine hereditability
      • First degree relatives should also be offered testing

Management

  • Management is primarily prophylactic surgery (earlier rather than later)
    • Restorative proctocolectomy with ileo pouch anal anastomosis
  • Periodic upper GI endoscopy should be performed every few years for monitoring upper GI polyps (may catch lesions early enough for endoscopic removal)
  • Children with known FAP should be offered prophylactic surgery once they turn 16/leave school

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