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
- Bloods e.g. FBC, LFT (mets), TFTs (if thyroid mass)
- Genetic testing can be done to identify the causative mutation and determine hereditability
- First degree relatives should also be offered testing
- Other tests to consider would be
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