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